Merging upstream version 126.0.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

118 files changed, 12004 insertions, 5976 deletions

diff --git a/toolkit/crashreporter/CrashAnnotations.yaml b/toolkit/crashreporter/CrashAnnotations.yaml
index 8f6bb2e8c2..61da061768 100644
--- a/toolkit/crashreporter/CrashAnnotations.yaml
+++ b/toolkit/crashreporter/CrashAnnotations.yaml
@@ -753,6 +753,12 @@ QuotaManagerShutdownTimeout:
   type: string
   ping: true
 
+QuotaManagerStorageIsNetworkResource:
+  description: >
+    On Windows, this indicates if QM's base dir lives on a network resource.
+    It is the direct result of the Win32 API function PathIsNetworkPath.
+  type: boolean
+
 RDDProcessStatus:
   description: >
     Status of the RDD process, can be set to "Running" or "Destroyed"
diff --git a/toolkit/crashreporter/CrashSubmit.sys.mjs b/toolkit/crashreporter/CrashSubmit.sys.mjs
index 28647c5a83..72ff5dc30f 100644
--- a/toolkit/crashreporter/CrashSubmit.sys.mjs
+++ b/toolkit/crashreporter/CrashSubmit.sys.mjs
@@ -2,8 +2,6 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-import { FileUtils } from "resource://gre/modules/FileUtils.sys.mjs";
-
 const SUCCESS = "success";
 const FAILED = "failed";
 const SUBMITTING = "submitting";
@@ -13,81 +11,6 @@ const UUID_REGEX =
 const SUBMISSION_REGEX =
   /^bp-[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/i;
 
-// TODO: this is still synchronous; need an async INI parser to make it async
-function parseINIStrings(path) {
-  let file = new FileUtils.File(path);
-  let factory = Cc["@mozilla.org/xpcom/ini-parser-factory;1"].getService(
-    Ci.nsIINIParserFactory
-  );
-  let parser = factory.createINIParser(file);
-  let obj = {};
-  for (let key of parser.getKeys("Strings")) {
-    obj[key] = parser.getString("Strings", key);
-  }
-  return obj;
-}
-
-// Since we're basically re-implementing (with async) part of the crashreporter
-// client here, we'll just steal the strings we need from crashreporter.ini
-async function getL10nStrings() {
-  let path = PathUtils.join(
-    Services.dirsvc.get("GreD", Ci.nsIFile).path,
-    "crashreporter.ini"
-  );
-  let pathExists = await IOUtils.exists(path);
-
-  if (!pathExists) {
-    // we if we're on a mac
-    let parentDir = PathUtils.parent(path);
-    path = PathUtils.join(
-      parentDir,
-      "MacOS",
-      "crashreporter.app",
-      "Contents",
-      "Resources",
-      "crashreporter.ini"
-    );
-
-    let pathExists = await IOUtils.exists(path);
-
-    if (!pathExists) {
-      // This happens on Android where everything is in an APK.
-      // Android users can't see the contents of the submitted files
-      // anyway, so just hardcode some fallback strings.
-      return {
-        crashid: "Crash ID: %s",
-        reporturl: "You can view details of this crash at %s",
-      };
-    }
-  }
-
-  let crstrings = parseINIStrings(path);
-  let strings = {
-    crashid: crstrings.CrashID,
-    reporturl: crstrings.CrashDetailsURL,
-  };
-
-  path = PathUtils.join(
-    Services.dirsvc.get("XCurProcD", Ci.nsIFile).path,
-    "crashreporter-override.ini"
-  );
-  pathExists = await IOUtils.exists(path);
-
-  if (pathExists) {
-    crstrings = parseINIStrings(path);
-
-    if ("CrashID" in crstrings) {
-      strings.crashid = crstrings.CrashID;
-    }
-
-    if ("CrashDetailsURL" in crstrings) {
-      strings.reporturl = crstrings.CrashDetailsURL;
-    }
-  }
-
-  return strings;
-}
-
 function getDir(name) {
   let uAppDataPath = Services.dirsvc.get("UAppData", Ci.nsIFile).path;
   return PathUtils.join(uAppDataPath, "Crash Reports", name);
@@ -109,11 +32,17 @@ function getPendingMinidump(id) {
 }
 
 async function writeSubmittedReportAsync(crashID, viewURL) {
-  let strings = await getL10nStrings();
-  let data = strings.crashid.replace("%s", crashID);
-
+  // Since we're basically re-implementing (with async) part of the
+  // crashreporter client here, we'll use the strings we need from the
+  // crashreporter fluent file.
+  const l10n = new Localization(["crashreporter/crashreporter.ftl"]);
+  let data = await l10n.formatValue("crashreporter-crash-identifier", {
+    id: crashID,
+  });
   if (viewURL) {
-    data += "\n" + strings.reporturl.replace("%s", viewURL);
+    data +=
+      "\n" +
+      (await l10n.formatValue("crashreporter-crash-details", { url: viewURL }));
   }
 
   await writeFileAsync("submitted", `${crashID}.txt`, data);
@@ -259,7 +188,7 @@ Submitter.prototype = {
     let manager = Services.crashmanager;
     let submissionID = manager.generateSubmissionID();
 
-    xhr.addEventListener("readystatechange", evt => {
+    xhr.addEventListener("readystatechange", () => {
       if (xhr.readyState == 4) {
         let ret =
           xhr.status === 200 ? this.parseResponse(xhr.responseText) : {};
diff --git a/toolkit/crashreporter/client/Throbber-small.avi b/toolkit/crashreporter/client/Throbber-small.avi
deleted file mode 100644
index 640ea62c0e..0000000000
--- a/toolkit/crashreporter/client/Throbber-small.avi
+++ /dev/null
diff --git a/toolkit/crashreporter/client/Throbber-small.gif b/toolkit/crashreporter/client/Throbber-small.gif
deleted file mode 100644
index cce32f20f4..0000000000
--- a/toolkit/crashreporter/client/Throbber-small.gif
+++ /dev/null
diff --git a/toolkit/crashreporter/client/app/Cargo.toml b/toolkit/crashreporter/client/app/Cargo.toml
new file mode 100644
index 0000000000..381ed32f97
--- /dev/null
+++ b/toolkit/crashreporter/client/app/Cargo.toml
@@ -0,0 +1,66 @@
+[package]
+name = "crashreporter"
+version = "1.0.0"
+edition = "2021"
+
+[[bin]]
+name = "crashreporter"
+
+[dependencies]
+anyhow = "1.0"
+cfg-if = "1.0"
+env_logger = { version = "0.10", default-features = false }
+fluent = "0.16.0"
+intl-memoizer = "0.5"
+libloading = "0.7"
+log = "0.4.17"
+mozbuild = "0.1"
+mozilla-central-workspace-hack = { version = "0.1", features = ["crashreporter"], optional = true }
+once_cell = "1"
+phf = "0.11"
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+sha2 = "0.10"
+time = { version = "0.3", features = ["formatting", "serde"] }
+unic-langid = { version = "0.9.1" }
+uuid = { version = "1", features = ["v4", "serde"] }
+zip = { version = "0.6", default-features = false }
+
+[target."cfg(target_os = \"macos\")".dependencies]
+block = "0.1"
+cocoa = { package = "cocoabind", path = "../cocoabind" }
+objc = "0.2"
+
+[target."cfg(target_os = \"linux\")".dependencies]
+gtk = { package = "gtkbind", path = "../gtkbind" }
+
+[target."cfg(target_os = \"windows\")".dependencies.windows-sys]
+version = "0.52"
+features = [
+    "Win32_Foundation",
+    "Win32_Globalization",
+    "Win32_Graphics_Gdi",
+    "Win32_System_Com",
+    "Win32_System_LibraryLoader",
+    "Win32_System_SystemServices",
+    "Win32_System_Threading",
+    "Win32_UI_Controls",
+    "Win32_UI_Input_KeyboardAndMouse",
+    "Win32_UI_Shell",
+    "Win32_UI_WindowsAndMessaging"
+]
+
+[features]
+# Required for tests
+mock = []
+
+[build-dependencies]
+embed-manifest = "1.4"
+mozbuild = "0.1"
+phf_codegen = "0.11"
+yaml-rust = "0.4"
+
+[dev-dependencies]
+bytes = "1.4"
+tokio = { version = "1.29", features = ["rt", "net", "time", "sync"] }
+warp = { version = "0.3", default-features = false }
diff --git a/toolkit/crashreporter/client/Makefile.in b/toolkit/crashreporter/client/app/Makefile.in
index 2d3ef1bee9..39fa3c8fbb 100644
--- a/toolkit/crashreporter/client/Makefile.in
+++ b/toolkit/crashreporter/client/app/Makefile.in
@@ -3,17 +3,15 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-ifeq ($(OS_ARCH),WINNT)
-MOZ_WINCONSOLE = 0
-endif
+ifeq ($(OS_ARCH),Darwin)
 
 include $(topsrcdir)/config/rules.mk
 
-ifeq ($(OS_ARCH),Darwin)
 libs::
 	$(NSINSTALL) -D $(DIST)/bin/crashreporter.app
-	rsync -a -C --exclude '*.in' $(srcdir)/macbuild/Contents $(DIST)/bin/crashreporter.app 
-	$(call py_action,preprocessor crashreporter.app/Contents/Resources/English.lproj/InfoPlist.strings,-Fsubstitution --output-encoding utf-16 -DAPP_NAME='$(MOZ_APP_DISPLAYNAME)' $(srcdir)/macbuild/Contents/Resources/English.lproj/InfoPlist.strings.in -o $(DIST)/bin/crashreporter.app/Contents/Resources/English.lproj/InfoPlist.strings)
+	rsync --archive --cvs-exclude --exclude '*.in' $(srcdir)/macos_app_bundle/ $(DIST)/bin/crashreporter.app/Contents/
+	$(call py_action,preprocessor crashreporter.app/Contents/Resources/English.lproj/InfoPlist.strings,-Fsubstitution --output-encoding utf-16 -DAPP_NAME='$(MOZ_APP_DISPLAYNAME)' $(srcdir)/macos_app_bundle/Resources/English.lproj/InfoPlist.strings.in -o $(DIST)/bin/crashreporter.app/Contents/Resources/English.lproj/InfoPlist.strings)
 	$(NSINSTALL) -D $(DIST)/bin/crashreporter.app/Contents/MacOS
 	$(NSINSTALL) $(DIST)/bin/crashreporter $(DIST)/bin/crashreporter.app/Contents/MacOS
+
 endif
diff --git a/toolkit/crashreporter/client/app/build.rs b/toolkit/crashreporter/client/app/build.rs
new file mode 100644
index 0000000000..98f20dc375
--- /dev/null
+++ b/toolkit/crashreporter/client/app/build.rs
@@ -0,0 +1,89 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use std::{env, path::Path};
+
+fn main() {
+    windows_manifest();
+    crash_ping_annotations();
+    set_mock_cfg();
+}
+
+fn windows_manifest() {
+    use embed_manifest::{embed_manifest, manifest, new_manifest};
+
+    if std::env::var_os("CARGO_CFG_WINDOWS").is_none() {
+        return;
+    }
+
+    // See https://docs.rs/embed-manifest/1.4.0/embed_manifest/fn.new_manifest.html for what the
+    // default manifest includes. The defaults include almost all of the settings used in the old
+    // crash reporter.
+    let manifest = new_manifest("CrashReporter")
+        // Use legacy active code page because GDI doesn't support per-process UTF8 (and older
+        // win10 may not support this setting anyway).
+        .active_code_page(manifest::ActiveCodePage::Legacy)
+        // GDI scaling is not enabled by default but we need it to make the GDI-drawn text look
+        // nice on high-DPI displays.
+        .gdi_scaling(manifest::Setting::Enabled);
+
+    embed_manifest(manifest).expect("unable to embed windows manifest file");
+
+    println!("cargo:rerun-if-changed=build.rs");
+}
+
+/// Generate crash ping annotation information from the yaml definition file.
+fn crash_ping_annotations() {
+    use std::fs::File;
+    use std::io::{BufWriter, Write};
+    use yaml_rust::{Yaml, YamlLoader};
+
+    let crash_annotations = Path::new("../../CrashAnnotations.yaml")
+        .canonicalize()
+        .unwrap();
+    println!("cargo:rerun-if-changed={}", crash_annotations.display());
+
+    let crash_ping_file = Path::new(&env::var("OUT_DIR").unwrap()).join("ping_annotations.rs");
+
+    let yaml = std::fs::read_to_string(crash_annotations).unwrap();
+    let Yaml::Hash(entries) = YamlLoader::load_from_str(&yaml)
+        .unwrap()
+        .into_iter()
+        .next()
+        .unwrap()
+    else {
+        panic!("unexpected crash annotations root type");
+    };
+
+    let ping_annotations = entries.into_iter().filter_map(|(k, v)| {
+        v["ping"]
+            .as_bool()
+            .unwrap_or(false)
+            .then(|| k.into_string().unwrap())
+    });
+
+    let mut phf_set = phf_codegen::Set::new();
+    for annotation in ping_annotations {
+        phf_set.entry(annotation);
+    }
+
+    let mut file = BufWriter::new(File::create(&crash_ping_file).unwrap());
+    writeln!(
+        &mut file,
+        "static PING_ANNOTATIONS: phf::Set<&'static str> = {};",
+        phf_set.build()
+    )
+    .unwrap();
+}
+
+/// Set the mock configuration option when tests are enabled or when the mock feature is enabled.
+fn set_mock_cfg() {
+    // Very inconveniently, there's no way to detect `cfg(test)` from build scripts. See
+    // https://github.com/rust-lang/cargo/issues/4789. This seems like an arbitrary and pointless
+    // limitation, and only complicates the evaluation of mock behavior. Because of this, we have a
+    // `mock` feature which is activated by `toolkit/library/rust/moz.build`.
+    if env::var_os("CARGO_FEATURE_MOCK").is_some() || mozbuild::config::MOZ_CRASHREPORTER_MOCK {
+        println!("cargo:rustc-cfg=mock");
+    }
+}
diff --git a/toolkit/crashreporter/client/macbuild/Contents/Info.plist b/toolkit/crashreporter/client/app/macos_app_bundle/Info.plist
index 51d6c4de37..f1679a922e 100644
--- a/toolkit/crashreporter/client/macbuild/Contents/Info.plist
+++ b/toolkit/crashreporter/client/app/macos_app_bundle/Info.plist
@@ -24,8 +24,6 @@
 	<string>1.0</string>
 	<key>LSHasLocalizedDisplayName</key>
 	<true/>
-	<key>NSMainNibFile</key>
-	<string>MainMenu</string>
 	<key>NSRequiresAquaSystemAppearance</key>
 	<false/>
 	<key>NSPrincipalClass</key>
diff --git a/toolkit/crashreporter/client/macbuild/Contents/PkgInfo b/toolkit/crashreporter/client/app/macos_app_bundle/PkgInfo
index cae6d0a58f..cae6d0a58f 100644
--- a/toolkit/crashreporter/client/macbuild/Contents/PkgInfo
+++ b/toolkit/crashreporter/client/app/macos_app_bundle/PkgInfo
diff --git a/toolkit/crashreporter/client/macbuild/Contents/Resources/English.lproj/InfoPlist.strings.in b/toolkit/crashreporter/client/app/macos_app_bundle/Resources/English.lproj/InfoPlist.strings.in
index e08ce59eb6..e08ce59eb6 100644
--- a/toolkit/crashreporter/client/macbuild/Contents/Resources/English.lproj/InfoPlist.strings.in
+++ b/toolkit/crashreporter/client/app/macos_app_bundle/Resources/English.lproj/InfoPlist.strings.in
diff --git a/toolkit/crashreporter/client/macbuild/Contents/Resources/crashreporter.icns b/toolkit/crashreporter/client/app/macos_app_bundle/Resources/crashreporter.icns
index 341cd05a4d..341cd05a4d 100644
--- a/toolkit/crashreporter/client/macbuild/Contents/Resources/crashreporter.icns
+++ b/toolkit/crashreporter/client/app/macos_app_bundle/Resources/crashreporter.icns
diff --git a/toolkit/crashreporter/client/app/moz.build b/toolkit/crashreporter/client/app/moz.build
new file mode 100644
index 0000000000..6e5c19173f
--- /dev/null
+++ b/toolkit/crashreporter/client/app/moz.build
@@ -0,0 +1,7 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+RUST_PROGRAMS = ["crashreporter"]
diff --git a/toolkit/crashreporter/client/app/src/async_task.rs b/toolkit/crashreporter/client/app/src/async_task.rs
new file mode 100644
index 0000000000..839db5e562
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/async_task.rs
@@ -0,0 +1,31 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Manage work across multiple threads.
+//!
+//! Each thread has thread-bound data which can be accessed in queued task functions.
+
+pub type TaskFn<T> = Box<dyn FnOnce(&T) + Send + 'static>;
+
+pub struct AsyncTask<T> {
+    send: Box<dyn Fn(TaskFn<T>) + Send + Sync>,
+}
+
+impl<T> AsyncTask<T> {
+    pub fn new<F: Fn(TaskFn<T>) + Send + Sync + 'static>(send: F) -> Self {
+        AsyncTask {
+            send: Box::new(send),
+        }
+    }
+
+    pub fn push<F: FnOnce(&T) + Send + 'static>(&self, f: F) {
+        (self.send)(Box::new(f));
+    }
+
+    pub fn wait<R: Send + 'static, F: FnOnce(&T) -> R + Send + 'static>(&self, f: F) -> R {
+        let (tx, rx) = std::sync::mpsc::sync_channel(0);
+        self.push(move |v| tx.send(f(v)).unwrap());
+        rx.recv().unwrap()
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/config.rs b/toolkit/crashreporter/client/app/src/config.rs
new file mode 100644
index 0000000000..4e919395e2
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/config.rs
@@ -0,0 +1,527 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+//! Application configuration.
+
+use crate::std::borrow::Cow;
+use crate::std::ffi::{OsStr, OsString};
+use crate::std::path::{Path, PathBuf};
+use crate::{lang, logging::LogTarget, std};
+use anyhow::Context;
+
+/// The number of the most recent minidump files to retain when pruning.
+const MINIDUMP_PRUNE_SAVE_COUNT: usize = 10;
+
+#[cfg(test)]
+pub mod test {
+    pub const MINIDUMP_PRUNE_SAVE_COUNT: usize = super::MINIDUMP_PRUNE_SAVE_COUNT;
+}
+
+const VENDOR_KEY: &str = "Vendor";
+const PRODUCT_KEY: &str = "ProductName";
+const DEFAULT_VENDOR: &str = "Mozilla";
+const DEFAULT_PRODUCT: &str = "Firefox";
+
+#[derive(Default)]
+pub struct Config {
+    /// Whether reports should be automatically submitted.
+    pub auto_submit: bool,
+    /// Whether all threads of the process should be dumped (versus just the crashing thread).
+    pub dump_all_threads: bool,
+    /// Whether to delete the dump files after submission.
+    pub delete_dump: bool,
+    /// The data directory.
+    pub data_dir: Option<PathBuf>,
+    /// The events directory.
+    pub events_dir: Option<PathBuf>,
+    /// The ping directory.
+    pub ping_dir: Option<PathBuf>,
+    /// The dump file.
+    ///
+    /// If missing, an error dialog is displayed.
+    pub dump_file: Option<PathBuf>,
+    /// The XUL_APP_FILE to define if restarting the application.
+    pub app_file: Option<OsString>,
+    /// The path to the application to use when restarting the crashed process.
+    pub restart_command: Option<OsString>,
+    /// The arguments to pass if restarting the application.
+    pub restart_args: Vec<OsString>,
+    /// The URL to which to send reports.
+    pub report_url: Option<OsString>,
+    /// The localized strings to use.
+    pub strings: Option<lang::LangStrings>,
+    /// The log target.
+    pub log_target: Option<LogTarget>,
+}
+
+pub struct ConfigStringBuilder<'a>(lang::LangStringBuilder<'a>);
+
+impl<'a> ConfigStringBuilder<'a> {
+    /// Set an argument for the string.
+    pub fn arg<V: Into<Cow<'a, str>>>(self, key: &'a str, value: V) -> Self {
+        ConfigStringBuilder(self.0.arg(key, value))
+    }
+
+    /// Get the localized string.
+    pub fn get(self) -> String {
+        self.0
+            .get()
+            .context("failed to get localized string")
+            .unwrap()
+    }
+}
+
+impl Config {
+    /// Return a configuration with no values set, and all bool values false.
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Load a configuration from the application environment.
+    #[cfg_attr(mock, allow(unused))]
+    pub fn read_from_environment(&mut self) -> anyhow::Result<()> {
+        /// Most environment variables are prefixed with `MOZ_CRASHREPORTER_`.
+        macro_rules! ekey {
+            ( $name:literal ) => {
+                concat!("MOZ_CRASHREPORTER_", $name)
+            };
+        }
+
+        self.auto_submit = env_bool(ekey!("AUTO_SUBMIT"));
+        self.dump_all_threads = env_bool(ekey!("DUMP_ALL_THREADS"));
+        self.delete_dump = !env_bool(ekey!("NO_DELETE_DUMP"));
+        self.data_dir = env_path(ekey!("DATA_DIRECTORY"));
+        self.events_dir = env_path(ekey!("EVENTS_DIRECTORY"));
+        self.ping_dir = env_path(ekey!("PING_DIRECTORY"));
+        self.app_file = std::env::var_os(ekey!("RESTART_XUL_APP_FILE"));
+
+        // Only support `MOZ_APP_LAUNCHER` on linux and macos.
+        if cfg!(not(target_os = "windows")) {
+            self.restart_command = std::env::var_os("MOZ_APP_LAUNCHER");
+        }
+
+        if self.restart_command.is_none() {
+            self.restart_command = Some(
+                self.sibling_program_path(mozbuild::config::MOZ_APP_NAME)
+                    .into(),
+            )
+        }
+
+        // We no longer use don't use `MOZ_CRASHREPORTER_RESTART_ARG_0`, see bug 1872920.
+        self.restart_args = (1..)
+            .into_iter()
+            .map_while(|arg_num| std::env::var_os(format!("{}_{}", ekey!("RESTART_ARG"), arg_num)))
+            // Sometimes these are empty, in which case they should be ignored.
+            .filter(|s| !s.is_empty())
+            .collect();
+
+        self.report_url = std::env::var_os(ekey!("URL"));
+
+        let mut args = std::env::args_os()
+            // skip program name
+            .skip(1);
+        self.dump_file = args.next().map(|p| p.into());
+        while let Some(arg) = args.next() {
+            log::warn!("ignoring extraneous argument: {}", arg.to_string_lossy());
+        }
+
+        self.strings = Some(lang::load().context("failed to load localized strings")?);
+
+        Ok(())
+    }
+
+    /// Get the localized string for the given index.
+    pub fn string(&self, index: &str) -> String {
+        self.build_string(index).get()
+    }
+
+    /// Build the localized string for the given index.
+    pub fn build_string<'a>(&'a self, index: &'a str) -> ConfigStringBuilder<'a> {
+        ConfigStringBuilder(
+            self.strings
+                .as_ref()
+                .expect("strings not set")
+                .builder(index),
+        )
+    }
+
+    /// Whether the configured language has right-to-left text flow.
+    pub fn is_rtl(&self) -> bool {
+        self.strings
+            .as_ref()
+            .map(|s| s.is_rtl())
+            .unwrap_or_default()
+    }
+
+    /// Load the extra file, updating configuration.
+    pub fn load_extra_file(&mut self) -> anyhow::Result<serde_json::Value> {
+        let extra_file = self.extra_file().unwrap();
+
+        // Load the extra file (which minidump-analyzer just updated).
+        let extra: serde_json::Value =
+            serde_json::from_reader(std::fs::File::open(&extra_file).with_context(|| {
+                self.build_string("crashreporter-error-opening-file")
+                    .arg("path", extra_file.display().to_string())
+                    .get()
+            })?)
+            .with_context(|| {
+                self.build_string("crashreporter-error-loading-file")
+                    .arg("path", extra_file.display().to_string())
+                    .get()
+            })?;
+
+        // Set report url if not already set.
+        if self.report_url.is_none() {
+            if let Some(url) = extra["ServerURL"].as_str() {
+                self.report_url = Some(url.into());
+            }
+        }
+
+        // Set the data dir if not already set.
+        if self.data_dir.is_none() {
+            let vendor = extra[VENDOR_KEY].as_str().unwrap_or(DEFAULT_VENDOR);
+            let product = extra[PRODUCT_KEY].as_str().unwrap_or(DEFAULT_PRODUCT);
+            self.data_dir = Some(self.get_data_dir(vendor, product)?);
+        }
+
+        // Clear the restart command if WER handled the crash. This prevents restarting the
+        // program. See bug 1872920.
+        if extra.get("WindowsErrorReporting").is_some() {
+            self.restart_command = None;
+        }
+
+        Ok(extra)
+    }
+
+    /// Get the path to the extra file.
+    ///
+    /// Returns None if no dump_file is set.
+    pub fn extra_file(&self) -> Option<PathBuf> {
+        self.dump_file.clone().map(extra_file_for_dump_file)
+    }
+
+    /// Get the path to the memory file.
+    ///
+    /// Returns None if no dump_file is set or if the memory file does not exist.
+    pub fn memory_file(&self) -> Option<PathBuf> {
+        self.dump_file.clone().and_then(|p| {
+            let p = memory_file_for_dump_file(p);
+            p.exists().then_some(p)
+        })
+    }
+
+    /// The path to the data directory.
+    ///
+    /// Panics if no data directory is set.
+    pub fn data_dir(&self) -> &Path {
+        self.data_dir.as_deref().unwrap()
+    }
+
+    /// The path to the dump file.
+    ///
+    /// Panics if no dump file is set.
+    pub fn dump_file(&self) -> &Path {
+        self.dump_file.as_deref().unwrap()
+    }
+
+    /// The id of the local dump file (the base filename without extension).
+    ///
+    /// Panics if no dump file is set.
+    pub fn local_dump_id(&self) -> Cow<str> {
+        self.dump_file().file_stem().unwrap().to_string_lossy()
+    }
+
+    /// Move crash data to the pending folder.
+    pub fn move_crash_data_to_pending(&mut self) -> anyhow::Result<()> {
+        let pending_crashes_dir = self.data_dir().join("pending");
+        std::fs::create_dir_all(&pending_crashes_dir).with_context(|| {
+            self.build_string("crashreporter-error-creating-dir")
+                .arg("path", pending_crashes_dir.display().to_string())
+                .get()
+        })?;
+
+        let move_file = |from: &Path| -> anyhow::Result<PathBuf> {
+            let to = pending_crashes_dir.join(from.file_name().unwrap());
+            std::fs::rename(from, &to).with_context(|| {
+                self.build_string("crashreporter-error-moving-path")
+                    .arg("from", from.display().to_string())
+                    .arg("to", to.display().to_string())
+                    .get()
+            })?;
+            Ok(to)
+        };
+
+        let new_dump_file = move_file(self.dump_file())?;
+        move_file(self.extra_file().unwrap().as_ref())?;
+        // Failing to move the memory file is recoverable.
+        if let Some(memory_file) = self.memory_file() {
+            if let Err(e) = move_file(memory_file.as_ref()) {
+                log::warn!("failed to move memory file: {e}");
+                if let Err(e) = std::fs::remove_file(&memory_file) {
+                    log::warn!("failed to remove {}: {e}", memory_file.display());
+                }
+            }
+        }
+
+        self.dump_file = Some(new_dump_file);
+
+        Ok(())
+    }
+
+    /// Form the path which signals EOL for a particular version.
+    pub fn version_eol_file(&self, version: &str) -> PathBuf {
+        self.data_dir().join(format!("EndOfLife{version}"))
+    }
+
+    /// Return the path used to store submitted crash ids.
+    pub fn submitted_crash_dir(&self) -> PathBuf {
+        self.data_dir().join("submitted")
+    }
+
+    /// Delete files related to the crash report.
+    pub fn delete_files(&self) {
+        if !self.delete_dump {
+            return;
+        }
+
+        for file in [&self.dump_file, &self.extra_file(), &self.memory_file()]
+            .into_iter()
+            .flatten()
+        {
+            if let Err(e) = std::fs::remove_file(file) {
+                log::warn!("failed to remove {}: {e}", file.display());
+            }
+        }
+    }
+
+    /// Prune old minidump files adjacent to the dump file.
+    pub fn prune_files(&self) -> anyhow::Result<()> {
+        log::info!("pruning minidump files to the {MINIDUMP_PRUNE_SAVE_COUNT} most recent");
+        let Some(file) = &self.dump_file else {
+            anyhow::bail!("no dump file")
+        };
+        let Some(dir) = file.parent() else {
+            anyhow::bail!("no parent directory for dump file")
+        };
+        log::debug!("pruning {} directory", dir.display());
+        let read_dir = dir.read_dir().with_context(|| {
+            format!(
+                "failed to read dump file parent directory {}",
+                dir.display()
+            )
+        })?;
+
+        let mut minidump_files = Vec::new();
+        for entry in read_dir {
+            match entry {
+                Err(e) => log::error!(
+                    "error while iterating over {} directory entry: {e}",
+                    dir.display()
+                ),
+                Ok(e) if e.path().extension() == Some("dmp".as_ref()) => {
+                    // Return if the metadata can't be read, since not being able to get metadata
+                    // for any file could make the selection of minidumps to delete incorrect.
+                    let meta = e.metadata().with_context(|| {
+                        format!("failed to read metadata for {}", e.path().display())
+                    })?;
+                    if meta.is_file() {
+                        let modified_time =
+                            meta.modified().expect(
+                                "file modification time should be available on all crashreporter platforms",
+                            );
+                        minidump_files.push((modified_time, e.path()));
+                    }
+                }
+                _ => (),
+            }
+        }
+
+        // Sort by modification time first, then path (just to have a defined behavior in the case
+        // of identical times). The reverse leaves the files in order from newest to oldest.
+        minidump_files.sort_unstable_by(|a, b| a.cmp(b).reverse());
+
+        // Delete files, skipping the most recent MINIDUMP_PRUNE_SAVE_COUNT.
+        for dump_file in minidump_files
+            .into_iter()
+            .skip(MINIDUMP_PRUNE_SAVE_COUNT)
+            .map(|v| v.1)
+        {
+            log::debug!("pruning {} and related files", dump_file.display());
+            if let Err(e) = std::fs::remove_file(&dump_file) {
+                log::warn!("failed to delete {}: {e}", dump_file.display());
+            }
+
+            // Ignore errors for the extra file and the memory file: they may not exist.
+            let _ = std::fs::remove_file(extra_file_for_dump_file(dump_file.clone()));
+            let _ = std::fs::remove_file(memory_file_for_dump_file(dump_file));
+        }
+        Ok(())
+    }
+
+    /// Get the path of a program that is a sibling of the crashreporter.
+    ///
+    /// On MacOS, this assumes that the crashreporter is its own application bundle within the main
+    /// program bundle. On other platforms this assumes siblings reside in the same directory as
+    /// the crashreporter.
+    ///
+    /// The returned path isn't guaranteed to exist.
+    // This method could be standalone rather than living in `Config`; it's here because it makes
+    // sense that if it were to rely on anything, it would be the `Config` (and that may change in
+    // the future).
+    pub fn sibling_program_path<N: AsRef<OsStr>>(&self, program: N) -> PathBuf {
+        // Expect shouldn't ever panic here because we need more than one argument to run
+        // the program in the first place (we've already previously iterated args).
+        //
+        // We use argv[0] rather than `std::env::current_exe` because `current_exe` doesn't define
+        // how symlinks are treated, and we want to support running directly from the local build
+        // directory (which uses symlinks on linux and macos).
+        let self_path = PathBuf::from(std::env::args_os().next().expect("failed to get argv[0]"));
+        let exe_extension = self_path.extension().unwrap_or_default();
+
+        let mut program_path = self_path.clone();
+        // Pop the executable off to get the parent directory.
+        program_path.pop();
+        program_path.push(program.as_ref());
+        program_path.set_extension(exe_extension);
+
+        if !program_path.exists() && cfg!(all(not(mock), target_os = "macos")) {
+            // On macOS the crash reporter client is shipped as an application bundle contained
+            // within Firefox's main application bundle. So when it's invoked its current working
+            // directory looks like:
+            // Firefox.app/Contents/MacOS/crashreporter.app/Contents/MacOS/
+            // The other applications we ship with Firefox are stored in the main bundle
+            // (Firefox.app/Contents/MacOS/) so we we need to go back three directories
+            // to reach them.
+
+            // 4 pops: 1 for the path that was just pushed, and 3 more for
+            // `crashreporter.app/Contents/MacOS`.
+            for _ in 0..4 {
+                program_path.pop();
+            }
+            program_path.push(program.as_ref());
+            program_path.set_extension(exe_extension);
+        }
+
+        program_path
+    }
+
+    cfg_if::cfg_if! {
+        if #[cfg(mock)] {
+            fn get_data_dir(&self, vendor: &str, product: &str) -> anyhow::Result<PathBuf> {
+                let mut path = PathBuf::from("data_dir");
+                path.push(vendor);
+                path.push(product);
+                path.push("Crash Reports");
+                Ok(path)
+            }
+        } else if #[cfg(target_os = "linux")] {
+            fn get_data_dir(&self, vendor: &str, product: &str) -> anyhow::Result<PathBuf> {
+                // home_dir is deprecated due to incorrect behavior on windows, but we only use it on linux
+                #[allow(deprecated)]
+                let mut data_path =
+                    std::env::home_dir().with_context(|| self.string("crashreporter-error-no-home-dir"))?;
+                data_path.push(format!(".{}", vendor.to_lowercase()));
+                data_path.push(product.to_lowercase());
+                data_path.push("Crash Reports");
+                Ok(data_path)
+            }
+        } else if #[cfg(target_os = "macos")] {
+            fn get_data_dir(&self, _vendor: &str, product: &str) -> anyhow::Result<PathBuf> {
+                use objc::{
+                    rc::autoreleasepool,
+                    runtime::{Object, BOOL, YES},
+                    *,
+                };
+                #[link(name = "Foundation", kind = "framework")]
+                extern "system" {
+                    fn NSSearchPathForDirectoriesInDomains(
+                        directory: usize,
+                        domain_mask: usize,
+                        expand_tilde: BOOL,
+                    ) -> *mut Object /* NSArray<NSString*>* */;
+                }
+                #[allow(non_upper_case_globals)]
+                const NSApplicationSupportDirectory: usize = 14;
+                #[allow(non_upper_case_globals)]
+                const NSUserDomainMask: usize = 1;
+
+                let mut data_path = autoreleasepool(|| {
+                    let paths /* NSArray<NSString*>* */ = unsafe {
+                                NSSearchPathForDirectoriesInDomains(NSApplicationSupportDirectory, NSUserDomainMask, YES)
+                            };
+                    if paths.is_null() {
+                        anyhow::bail!("NSSearchPathForDirectoriesInDomains returned nil");
+                    }
+                    let path: *mut Object /* NSString* */ = unsafe { msg_send![paths, firstObject] };
+                    if path.is_null() {
+                        anyhow::bail!("NSSearchPathForDirectoriesInDomains returned no paths");
+                    }
+
+                    let str_pointer: *const i8 = unsafe { msg_send![path, UTF8String] };
+                    // # Safety
+                    // The pointer is a readable C string with a null terminator.
+                    let Ok(s) = unsafe { std::ffi::CStr::from_ptr(str_pointer) }.to_str() else {
+                        anyhow::bail!("NSString wasn't valid UTF8");
+                    };
+                    Ok(PathBuf::from(s))
+                })?;
+                data_path.push(product);
+                std::fs::create_dir_all(&data_path).with_context(|| {
+                    self.build_string("crashreporter-error-creating-dir")
+                        .arg("path", data_path.display().to_string())
+                        .get()
+                })?;
+                data_path.push("Crash Reports");
+                Ok(data_path)
+            }
+        } else if #[cfg(target_os = "windows")] {
+            fn get_data_dir(&self, vendor: &str, product: &str) -> anyhow::Result<PathBuf> {
+                use crate::std::os::windows::ffi::OsStringExt;
+                use windows_sys::{
+                    core::PWSTR,
+                    Win32::{
+                        Globalization::lstrlenW,
+                        System::Com::CoTaskMemFree,
+                        UI::Shell::{FOLDERID_RoamingAppData, SHGetKnownFolderPath},
+                    },
+                };
+
+                let mut path: PWSTR = std::ptr::null_mut();
+                let result = unsafe { SHGetKnownFolderPath(&FOLDERID_RoamingAppData, 0, 0, &mut path) };
+                if result != 0 {
+                    unsafe { CoTaskMemFree(path as _) };
+                    anyhow::bail!("failed to get known path for roaming appdata");
+                }
+
+                let length = unsafe { lstrlenW(path) };
+                let slice = unsafe { std::slice::from_raw_parts(path, length as usize) };
+                let osstr = OsString::from_wide(slice);
+                unsafe { CoTaskMemFree(path as _) };
+                let mut path = PathBuf::from(osstr);
+                path.push(vendor);
+                path.push(product);
+                path.push("Crash Reports");
+                Ok(path)
+            }
+        }
+    }
+}
+
+fn env_bool<K: AsRef<OsStr>>(name: K) -> bool {
+    std::env::var(name).map(|s| !s.is_empty()).unwrap_or(false)
+}
+
+fn env_path<K: AsRef<OsStr>>(name: K) -> Option<PathBuf> {
+    std::env::var_os(name).map(PathBuf::from)
+}
+
+fn extra_file_for_dump_file(mut dump_file: PathBuf) -> PathBuf {
+    dump_file.set_extension("extra");
+    dump_file
+}
+
+fn memory_file_for_dump_file(mut dump_file: PathBuf) -> PathBuf {
+    dump_file.set_extension("memory.json.gz");
+    dump_file
+}
diff --git a/toolkit/crashreporter/client/app/src/data.rs b/toolkit/crashreporter/client/app/src/data.rs
new file mode 100644
index 0000000000..474da8966a
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/data.rs
@@ -0,0 +1,400 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Data binding types are used to implement dynamic behaviors in UIs. [`Event`] is the primitive
+//! type underlying most others. [Properties](Property) are what should usually be used in UI
+//! models, since they have `From` impls allowing different binding behaviors to be set.
+
+use std::cell::RefCell;
+use std::rc::Rc;
+
+/// An event which can have multiple subscribers.
+///
+/// The type parameter is the payload of the event.
+pub struct Event<T> {
+    subscribers: Rc<RefCell<Vec<Box<dyn Fn(&T)>>>>,
+}
+
+impl<T> Clone for Event<T> {
+    fn clone(&self) -> Self {
+        Event {
+            subscribers: self.subscribers.clone(),
+        }
+    }
+}
+
+impl<T> Default for Event<T> {
+    fn default() -> Self {
+        Event {
+            subscribers: Default::default(),
+        }
+    }
+}
+
+impl<T> std::fmt::Debug for Event<T> {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        write!(
+            f,
+            "{} {{ {} subscribers }}",
+            std::any::type_name::<Self>(),
+            self.subscribers.borrow().len()
+        )
+    }
+}
+
+impl<T> Event<T> {
+    /// Add a callback for when the event is fired.
+    pub fn subscribe<F>(&self, f: F)
+    where
+        F: Fn(&T) + 'static,
+    {
+        self.subscribers.borrow_mut().push(Box::new(f));
+    }
+
+    /// Fire the event with the given payload.
+    pub fn fire(&self, payload: &T) {
+        for f in self.subscribers.borrow().iter() {
+            f(payload);
+        }
+    }
+}
+
+/// A synchronized runtime value.
+///
+/// Consumers can subscribe to change events on the value. Change events are fired when
+/// `borrow_mut()` references are dropped.
+#[derive(Default)]
+pub struct Synchronized<T> {
+    inner: Rc<SynchronizedInner<T>>,
+}
+
+impl<T> Clone for Synchronized<T> {
+    fn clone(&self) -> Self {
+        Synchronized {
+            inner: self.inner.clone(),
+        }
+    }
+}
+
+impl<T: std::fmt::Debug> std::fmt::Debug for Synchronized<T> {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        f.debug_struct(std::any::type_name::<Self>())
+            .field("current", &*self.inner.current.borrow())
+            .field("change", &self.inner.change)
+            .finish()
+    }
+}
+
+#[derive(Default)]
+struct SynchronizedInner<T> {
+    current: RefCell<T>,
+    change: Event<T>,
+}
+
+impl<T> Synchronized<T> {
+    /// Create a new value with the given inner data.
+    pub fn new(initial: T) -> Self {
+        Synchronized {
+            inner: Rc::new(SynchronizedInner {
+                current: RefCell::new(initial),
+                change: Default::default(),
+            }),
+        }
+    }
+
+    /// Borrow a value's data.
+    pub fn borrow(&self) -> std::cell::Ref<T> {
+        self.inner.current.borrow()
+    }
+
+    /// Mutably borrow a value's data.
+    ///
+    /// When the mutable reference is dropped, a change event is fired.
+    pub fn borrow_mut(&self) -> ValueRefMut<'_, T> {
+        ValueRefMut {
+            value: std::mem::ManuallyDrop::new(self.inner.current.borrow_mut()),
+            inner: &self.inner,
+        }
+    }
+
+    /// Subscribe to change events in the value.
+    pub fn on_change<F: Fn(&T) + 'static>(&self, f: F) {
+        self.inner.change.subscribe(f);
+    }
+
+    /// Update another synchronized value when this one changes.
+    pub fn update_on_change<U: 'static, F: Fn(&T) -> U + 'static>(
+        &self,
+        other: &Synchronized<U>,
+        f: F,
+    ) {
+        let other = other.clone();
+        self.on_change(move |val| {
+            *other.borrow_mut() = f(val);
+        });
+    }
+
+    /// Create a new synchronized value which will update when this one changes.
+    pub fn mapped<U: 'static, F: Fn(&T) -> U + 'static>(&self, f: F) -> Synchronized<U> {
+        let s = Synchronized::new(f(&*self.borrow()));
+        self.update_on_change(&s, f);
+        s
+    }
+
+    pub fn join<A: 'static, B: 'static, F: Fn(&A, &B) -> T + Clone + 'static>(
+        a: &Synchronized<A>,
+        b: &Synchronized<B>,
+        f: F,
+    ) -> Self
+    where
+        T: 'static,
+    {
+        let s = Synchronized::new(f(&*a.borrow(), &*b.borrow()));
+        let update = cc! { (a,b,s) move || {
+            *s.borrow_mut() = f(&*a.borrow(), &*b.borrow());
+        }};
+        a.on_change(cc! { (update) move |_| update()});
+        b.on_change(move |_| update());
+        s
+    }
+}
+
+/// A runtime value that can be fetched on-demand (read-only).
+///
+/// Consumers call [`read`] or [`get`] to retrieve the value, while producers call [`register`] to
+/// set the function which is called to retrieve the value. This is of most use for things like
+/// editable text strings, where it would be unnecessarily expensive to e.g. update a
+/// `Synchronized` property as the text string is changed (debouncing could be used, but if change
+/// notification isn't needed then it's still unnecessary).
+pub struct OnDemand<T> {
+    get: Rc<RefCell<Option<Box<dyn Fn(&mut T) + 'static>>>>,
+}
+
+impl<T> Default for OnDemand<T> {
+    fn default() -> Self {
+        OnDemand {
+            get: Default::default(),
+        }
+    }
+}
+
+impl<T> Clone for OnDemand<T> {
+    fn clone(&self) -> Self {
+        OnDemand {
+            get: self.get.clone(),
+        }
+    }
+}
+
+impl<T> std::fmt::Debug for OnDemand<T> {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        write!(
+            f,
+            "{} {{ {} }}",
+            std::any::type_name::<Self>(),
+            if self.get.borrow().is_none() {
+                "not registered"
+            } else {
+                "registered"
+            }
+        )
+    }
+}
+
+impl<T> OnDemand<T> {
+    /// Reads the current value.
+    pub fn read(&self, value: &mut T) {
+        match &*self.get.borrow() {
+            None => {
+                // The test UI doesn't always register OnDemand getters (only on a per-test basis),
+                // so don't panic otherwise the tests will fail unnecessarily.
+                #[cfg(not(test))]
+                panic!("OnDemand not registered by renderer")
+            }
+            Some(f) => f(value),
+        }
+    }
+
+    /// Get a copy of the current value.
+    pub fn get(&self) -> T
+    where
+        T: Default,
+    {
+        let mut r = T::default();
+        self.read(&mut r);
+        r
+    }
+
+    /// Register the function to use when getting the value.
+    pub fn register(&self, f: impl Fn(&mut T) + 'static) {
+        *self.get.borrow_mut() = Some(Box::new(f));
+    }
+}
+
+/// A UI element property.
+///
+/// Properties support static and dynamic value bindings.
+/// * `T` can be converted to static bindings.
+/// * `Synchronized<T>` can be converted to dynamic bindings which will be updated
+/// bidirectionally.
+/// * `OnDemand<T>` can be converted to dynamic bindings which can be queried on an as-needed
+/// basis.
+#[derive(Clone, Debug)]
+pub enum Property<T> {
+    Static(T),
+    Binding(Synchronized<T>),
+    ReadOnly(OnDemand<T>),
+}
+
+#[cfg(test)]
+impl<T: Clone + Default + 'static> Property<T> {
+    pub fn set(&self, value: T) {
+        match self {
+            Property::Static(_) => panic!("cannot set static property"),
+            Property::Binding(s) => *s.borrow_mut() = value,
+            Property::ReadOnly(o) => o.register(move |v| *v = value.clone()),
+        }
+    }
+
+    pub fn get(&self) -> T {
+        match self {
+            Property::Static(v) => v.clone(),
+            Property::Binding(s) => s.borrow().clone(),
+            Property::ReadOnly(o) => o.get(),
+        }
+    }
+}
+
+impl<T: Default> Default for Property<T> {
+    fn default() -> Self {
+        Property::Static(Default::default())
+    }
+}
+
+impl<T> From<T> for Property<T> {
+    fn from(value: T) -> Self {
+        Property::Static(value)
+    }
+}
+
+impl<T> From<&Synchronized<T>> for Property<T> {
+    fn from(value: &Synchronized<T>) -> Self {
+        Property::Binding(value.clone())
+    }
+}
+
+impl<T> From<&OnDemand<T>> for Property<T> {
+    fn from(value: &OnDemand<T>) -> Self {
+        Property::ReadOnly(value.clone())
+    }
+}
+
+/// A mutable Value reference.
+///
+/// When dropped, the Value's change event will fire (_after_ demoting the RefMut to a Ref).
+pub struct ValueRefMut<'a, T> {
+    value: std::mem::ManuallyDrop<std::cell::RefMut<'a, T>>,
+    inner: &'a SynchronizedInner<T>,
+}
+
+impl<T> std::ops::Deref for ValueRefMut<'_, T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        &*self.value
+    }
+}
+
+impl<T> std::ops::DerefMut for ValueRefMut<'_, T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut *self.value
+    }
+}
+
+impl<T> Drop for ValueRefMut<'_, T> {
+    fn drop(&mut self) {
+        unsafe { std::mem::ManuallyDrop::drop(&mut self.value) };
+        self.inner.change.fire(&*self.inner.current.borrow());
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use std::sync::atomic::{AtomicUsize, Ordering::Relaxed};
+
+    #[derive(Default, Clone)]
+    struct Trace {
+        count: Rc<AtomicUsize>,
+    }
+
+    impl Trace {
+        fn inc(&self) {
+            self.count.fetch_add(1, Relaxed);
+        }
+
+        fn set(&self, v: usize) {
+            self.count.store(v, Relaxed);
+        }
+
+        fn count(&self) -> usize {
+            self.count.load(Relaxed)
+        }
+    }
+
+    #[test]
+    fn event() {
+        let t1 = Trace::default();
+        let t2 = Trace::default();
+        let evt = Event::default();
+        evt.subscribe(cc! { (t1) move |x| {
+            assert!(x == &42);
+            t1.inc()
+        }});
+        evt.fire(&42);
+        assert_eq!(t1.count(), 1);
+        evt.subscribe(cc! { (t2) move |_| t2.inc() });
+        evt.fire(&42);
+        assert_eq!(t1.count(), 2);
+        assert_eq!(t2.count(), 1);
+    }
+
+    #[test]
+    fn synchronized() {
+        let t1 = Trace::default();
+        let s = Synchronized::<usize>::default();
+        assert_eq!(*s.borrow(), 0);
+
+        s.on_change(cc! { (t1) move |v| t1.set(*v) });
+        {
+            let mut s_ref = s.borrow_mut();
+            *s_ref = 41;
+            // Changes should only occur when the ref is dropped
+            assert_eq!(t1.count(), 0);
+            *s_ref = 42;
+        }
+        assert_eq!(t1.count(), 42);
+        assert_eq!(*s.borrow(), 42);
+    }
+
+    #[test]
+    fn ondemand() {
+        let t1 = Trace::default();
+        let d = OnDemand::<usize>::default();
+        d.register(|v| *v = 42);
+        {
+            let mut v = 0;
+            d.read(&mut v);
+            assert_eq!(v, 42);
+        }
+        d.register(|v| *v = 10);
+        assert_eq!(d.get(), 10);
+
+        t1.inc();
+        d.register(cc! { (t1) move |v| *v = t1.count() });
+        assert_eq!(d.get(), 1);
+        t1.set(42);
+        assert_eq!(d.get(), 42);
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/lang/language_info.rs b/toolkit/crashreporter/client/app/src/lang/language_info.rs
new file mode 100644
index 0000000000..b05953e2b3
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/lang/language_info.rs
@@ -0,0 +1,74 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+use super::LangStrings;
+use anyhow::Context;
+use fluent::{bundle::FluentBundle, FluentResource};
+use unic_langid::LanguageIdentifier;
+
+const FALLBACK_FTL_FILE: &str = include_str!(mozbuild::srcdir_path!(
+    "/toolkit/locales/en-US/crashreporter/crashreporter.ftl"
+));
+const FALLBACK_BRANDING_FILE: &str = include_str!(mozbuild::srcdir_path!(
+    "/browser/branding/official/locales/en-US/brand.ftl"
+));
+
+/// Localization language information.
+#[derive(Debug, Clone)]
+pub struct LanguageInfo {
+    pub identifier: String,
+    pub ftl_definitions: String,
+    pub ftl_branding: String,
+}
+
+impl Default for LanguageInfo {
+    fn default() -> Self {
+        Self::fallback()
+    }
+}
+
+impl LanguageInfo {
+    /// Get the fallback bundled language information (en-US).
+    pub fn fallback() -> Self {
+        LanguageInfo {
+            identifier: "en-US".to_owned(),
+            ftl_definitions: FALLBACK_FTL_FILE.to_owned(),
+            ftl_branding: FALLBACK_BRANDING_FILE.to_owned(),
+        }
+    }
+
+    /// Load strings from the language info.
+    pub fn load_strings(self) -> anyhow::Result<LangStrings> {
+        let Self {
+            identifier: lang,
+            ftl_definitions: definitions,
+            ftl_branding: branding,
+        } = self;
+
+        let langid = lang
+            .parse::<LanguageIdentifier>()
+            .with_context(|| format!("failed to parse language identifier ({lang})"))?;
+        let rtl = langid.character_direction() == unic_langid::CharacterDirection::RTL;
+        let mut bundle = FluentBundle::new_concurrent(vec![langid]);
+
+        fn add_ftl<M>(
+            bundle: &mut FluentBundle<FluentResource, M>,
+            ftl: String,
+        ) -> anyhow::Result<()> {
+            let resource = FluentResource::try_new(ftl)
+                .ok()
+                .context("failed to create fluent resource")?;
+            bundle
+                .add_resource(resource)
+                .ok()
+                .context("failed to add fluent resource to bundle")?;
+            Ok(())
+        }
+
+        add_ftl(&mut bundle, branding).context("failed to add branding")?;
+        add_ftl(&mut bundle, definitions).context("failed to add localization")?;
+
+        Ok(LangStrings::new(bundle, rtl))
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/lang/mod.rs b/toolkit/crashreporter/client/app/src/lang/mod.rs
new file mode 100644
index 0000000000..9b7495f92a
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/lang/mod.rs
@@ -0,0 +1,89 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+mod language_info;
+mod omnijar;
+
+use fluent::{bundle::FluentBundle, FluentArgs, FluentResource};
+use intl_memoizer::concurrent::IntlLangMemoizer;
+#[cfg(test)]
+pub use language_info::LanguageInfo;
+use std::borrow::Cow;
+use std::collections::BTreeMap;
+
+/// Get the localized string bundle.
+pub fn load() -> anyhow::Result<LangStrings> {
+    // TODO support langpacks, bug 1873210
+    omnijar::read().unwrap_or_else(|e| {
+        log::warn!("failed to read localization data from the omnijar ({e}), falling back to bundled content");
+        Default::default()
+    }).load_strings()
+}
+
+/// A bundle of localized strings.
+pub struct LangStrings {
+    bundle: FluentBundle<FluentResource, IntlLangMemoizer>,
+    rtl: bool,
+}
+
+/// Arguments to build a localized string.
+pub type LangStringsArgs<'a> = BTreeMap<&'a str, Cow<'a, str>>;
+
+impl LangStrings {
+    pub fn new(bundle: FluentBundle<FluentResource, IntlLangMemoizer>, rtl: bool) -> Self {
+        LangStrings { bundle, rtl }
+    }
+
+    /// Return whether the localized language has right-to-left text flow.
+    pub fn is_rtl(&self) -> bool {
+        self.rtl
+    }
+
+    pub fn get(&self, index: &str, args: LangStringsArgs) -> anyhow::Result<String> {
+        let mut fluent_args = FluentArgs::with_capacity(args.len());
+        for (k, v) in args {
+            fluent_args.set(k, v);
+        }
+
+        let Some(pattern) = self.bundle.get_message(index).and_then(|m| m.value()) else {
+            anyhow::bail!("failed to get fluent message for {index}");
+        };
+        let mut errs = Vec::new();
+        let ret = self
+            .bundle
+            .format_pattern(pattern, Some(&fluent_args), &mut errs);
+        if !errs.is_empty() {
+            anyhow::bail!("errors while formatting pattern: {errs:?}");
+        }
+        Ok(ret.into_owned())
+    }
+
+    pub fn builder<'a>(&'a self, index: &'a str) -> LangStringBuilder<'a> {
+        LangStringBuilder {
+            strings: self,
+            index,
+            args: Default::default(),
+        }
+    }
+}
+
+/// A localized string builder.
+pub struct LangStringBuilder<'a> {
+    strings: &'a LangStrings,
+    index: &'a str,
+    args: LangStringsArgs<'a>,
+}
+
+impl<'a> LangStringBuilder<'a> {
+    /// Set an argument for the string.
+    pub fn arg<V: Into<Cow<'a, str>>>(mut self, key: &'a str, value: V) -> Self {
+        self.args.insert(key, value.into());
+        self
+    }
+
+    /// Get the localized string.
+    pub fn get(self) -> anyhow::Result<String> {
+        self.strings.get(self.index, self.args)
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/lang/omnijar.rs b/toolkit/crashreporter/client/app/src/lang/omnijar.rs
new file mode 100644
index 0000000000..2d2c34dd8d
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/lang/omnijar.rs
@@ -0,0 +1,103 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use super::language_info::LanguageInfo;
+use crate::std::{
+    env::current_exe,
+    fs::File,
+    io::{BufRead, BufReader, Read},
+    path::Path,
+};
+use anyhow::Context;
+use zip::read::ZipArchive;
+
+/// Read the appropriate localization fluent definitions from the omnijar files.
+///
+/// Returns (locale name, fluent definitions).
+pub fn read() -> anyhow::Result<LanguageInfo> {
+    let mut path = current_exe().context("failed to get current executable")?;
+    path.pop();
+    path.push("omni.ja");
+
+    let mut zip = read_omnijar_file(&path)?;
+    let locales = {
+        let buf = BufReader::new(
+            zip.by_name("res/multilocale.txt")
+                .context("failed to read multilocale file in zip archive")?,
+        );
+        let line = buf
+            .lines()
+            .next()
+            .ok_or(anyhow::anyhow!("multilocale file was empty"))?
+            .context("failed to read first line of multilocale file")?;
+        line.split(",")
+            .map(|s| s.trim().to_owned())
+            .collect::<Vec<_>>()
+    };
+
+    let (locale, ftl_definitions) = 'defs: {
+        for locale in &locales {
+            match read_strings(locale, &mut zip) {
+                Ok(v) => break 'defs (locale.to_string(), v),
+                Err(e) => log::warn!("{e:#}"),
+            }
+        }
+        anyhow::bail!("failed to find any usable localized strings in the omnijar")
+    };
+
+    // The brand ftl is in the browser omnijar.
+    path.pop();
+    path.push("browser");
+    path.push("omni.ja");
+
+    let ftl_branding = 'branding: {
+        for locale in &locales {
+            match read_branding(&locale, &mut zip) {
+                Ok(v) => break 'branding v,
+                Err(e) => log::warn!("failed to read branding from omnijar: {e:#}"),
+            }
+        }
+        log::info!("using fallback branding info");
+        LanguageInfo::default().ftl_branding
+    };
+
+    Ok(LanguageInfo {
+        identifier: locale,
+        ftl_definitions,
+        ftl_branding,
+    })
+}
+
+/// Read the localized strings from the given zip archive (omnijar).
+fn read_strings(locale: &str, archive: &mut ZipArchive<File>) -> anyhow::Result<String> {
+    let mut file = archive
+        .by_name(&format!(
+            "localization/{locale}/crashreporter/crashreporter.ftl"
+        ))
+        .with_context(|| format!("failed to locate localization file for {locale}"))?;
+
+    let mut ftl_definitions = String::new();
+    file.read_to_string(&mut ftl_definitions)
+        .with_context(|| format!("failed to read localization file for {locale}"))?;
+
+    Ok(ftl_definitions)
+}
+
+/// Read the branding information from the given zip archive (omnijar).
+fn read_branding(locale: &str, archive: &mut ZipArchive<File>) -> anyhow::Result<String> {
+    let mut file = archive
+        .by_name(&format!("localization/{locale}/branding/brand.ftl"))
+        .with_context(|| format!("failed to locate branding localization file for {locale}"))?;
+    let mut s = String::new();
+    file.read_to_string(&mut s)
+        .with_context(|| format!("failed to read branding localization file for {locale}"))?;
+    Ok(s)
+}
+
+fn read_omnijar_file(path: &Path) -> anyhow::Result<ZipArchive<File>> {
+    ZipArchive::new(
+        File::open(&path).with_context(|| format!("failed to open {}", path.display()))?,
+    )
+    .with_context(|| format!("failed to read zip archive in {}", path.display()))
+}
diff --git a/toolkit/crashreporter/client/app/src/logging.rs b/toolkit/crashreporter/client/app/src/logging.rs
new file mode 100644
index 0000000000..c3f85312f8
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/logging.rs
@@ -0,0 +1,86 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+//! Application logging facilities.
+
+use crate::std::{
+    self,
+    path::Path,
+    sync::{Arc, Mutex},
+};
+
+/// Initialize logging and return a log target which can be used to change the destination of log
+/// statements.
+#[cfg_attr(mock, allow(unused))]
+pub fn init() -> LogTarget {
+    let log_target_inner = LogTargetInner::default();
+
+    env_logger::builder()
+        .parse_env(
+            env_logger::Env::new()
+                .filter("MOZ_CRASHEREPORTER")
+                .write_style("MOZ_CRASHREPORTER_STYLE"),
+        )
+        .target(env_logger::fmt::Target::Pipe(Box::new(
+            log_target_inner.clone(),
+        )))
+        .init();
+
+    LogTarget {
+        inner: log_target_inner,
+    }
+}
+
+/// Controls the target of logging.
+#[derive(Clone)]
+pub struct LogTarget {
+    inner: LogTargetInner,
+}
+
+impl LogTarget {
+    /// Set the file to which log statements will be written.
+    pub fn set_file(&self, path: &Path) {
+        match std::fs::File::create(path) {
+            Ok(file) => {
+                if let Ok(mut guard) = self.inner.target.lock() {
+                    *guard = Box::new(file);
+                }
+            }
+            Err(e) => log::error!("failed to retarget log to {}: {e}", path.display()),
+        }
+    }
+}
+
+/// A private inner class implements Write, allows creation, etc. Externally the `LogTarget` only
+/// supports changing the target and nothing else.
+#[derive(Clone)]
+struct LogTargetInner {
+    target: Arc<Mutex<Box<dyn std::io::Write + Send + 'static>>>,
+}
+
+impl Default for LogTargetInner {
+    fn default() -> Self {
+        LogTargetInner {
+            target: Arc::new(Mutex::new(Box::new(std::io::stderr()))),
+        }
+    }
+}
+
+impl std::io::Write for LogTargetInner {
+    fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
+        let Ok(mut guard) = self.target.lock() else {
+            // Pretend we wrote successfully.
+            return Ok(buf.len());
+        };
+        guard.write(buf)
+    }
+
+    fn flush(&mut self) -> std::io::Result<()> {
+        let Ok(mut guard) = self.target.lock() else {
+            // Pretend we flushed successfully.
+            return Ok(());
+        };
+        guard.flush()
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/logic.rs b/toolkit/crashreporter/client/app/src/logic.rs
new file mode 100644
index 0000000000..4ad1baa9c6
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/logic.rs
@@ -0,0 +1,660 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Business logic for the crash reporter.
+
+use crate::std::{
+    cell::RefCell,
+    path::PathBuf,
+    process::Command,
+    sync::{
+        atomic::{AtomicBool, Ordering::Relaxed},
+        Arc, Mutex,
+    },
+};
+use crate::{
+    async_task::AsyncTask,
+    config::Config,
+    net,
+    settings::Settings,
+    std,
+    ui::{ReportCrashUI, ReportCrashUIState, SubmitState},
+};
+use anyhow::Context;
+use uuid::Uuid;
+
+/// The main crash reporting logic.
+pub struct ReportCrash {
+    pub settings: RefCell<Settings>,
+    config: Arc<Config>,
+    extra: serde_json::Value,
+    settings_file: PathBuf,
+    attempted_to_send: AtomicBool,
+    ui: Option<AsyncTask<ReportCrashUIState>>,
+}
+
+impl ReportCrash {
+    pub fn new(config: Arc<Config>, extra: serde_json::Value) -> anyhow::Result<Self> {
+        let settings_file = config.data_dir().join("crashreporter_settings.json");
+        let settings: Settings = match std::fs::File::open(&settings_file) {
+            Err(e) if e.kind() != std::io::ErrorKind::NotFound => {
+                anyhow::bail!(
+                    "failed to open settings file ({}): {e}",
+                    settings_file.display()
+                );
+            }
+            Err(_) => Default::default(),
+            Ok(f) => Settings::from_reader(f)?,
+        };
+        Ok(ReportCrash {
+            config,
+            extra,
+            settings_file,
+            settings: settings.into(),
+            attempted_to_send: Default::default(),
+            ui: None,
+        })
+    }
+
+    /// Returns whether an attempt was made to send the report.
+    pub fn run(mut self) -> anyhow::Result<bool> {
+        self.set_log_file();
+        let hash = self.compute_minidump_hash().map(Some).unwrap_or_else(|e| {
+            log::warn!("failed to compute minidump hash: {e}");
+            None
+        });
+        let ping_uuid = self.send_crash_ping(hash.as_deref()).unwrap_or_else(|e| {
+            log::warn!("failed to send crash ping: {e}");
+            None
+        });
+        if let Err(e) = self.update_events_file(hash.as_deref(), ping_uuid) {
+            log::warn!("failed to update events file: {e}");
+        }
+        self.sanitize_extra();
+        self.check_eol_version()?;
+        if !self.config.auto_submit {
+            self.run_ui();
+        } else {
+            anyhow::ensure!(self.try_send().unwrap_or(false), "failed to send report");
+        }
+
+        Ok(self.attempted_to_send.load(Relaxed))
+    }
+
+    /// Set the log file based on the current configured paths.
+    ///
+    /// This is the earliest that this can occur as the configuration data dir may be set based on
+    /// fields in the extra file.
+    fn set_log_file(&self) {
+        if let Some(log_target) = &self.config.log_target {
+            log_target.set_file(&self.config.data_dir().join("submit.log"));
+        }
+    }
+
+    /// Compute the SHA256 hash of the minidump file contents, and return it as a hex string.
+    fn compute_minidump_hash(&self) -> anyhow::Result<String> {
+        let hash = {
+            use sha2::{Digest, Sha256};
+            let mut dump_file = std::fs::File::open(self.config.dump_file())?;
+            let mut hasher = Sha256::new();
+            std::io::copy(&mut dump_file, &mut hasher)?;
+            hasher.finalize()
+        };
+
+        let mut s = String::with_capacity(hash.len() * 2);
+        for byte in hash {
+            use crate::std::fmt::Write;
+            write!(s, "{:02x}", byte).unwrap();
+        }
+
+        Ok(s)
+    }
+
+    /// Send a crash ping to telemetry.
+    ///
+    /// Returns the crash ping uuid.
+    fn send_crash_ping(&self, minidump_hash: Option<&str>) -> anyhow::Result<Option<Uuid>> {
+        if self.config.ping_dir.is_none() {
+            log::warn!("not sending crash ping because no ping directory configured");
+            return Ok(None);
+        }
+
+        //TODO support glean crash pings (or change pingsender to do so)
+
+        let dump_id = self.config.local_dump_id();
+        let ping = net::legacy_telemetry::Ping::crash(&self.extra, dump_id.as_ref(), minidump_hash)
+            .context("failed to create telemetry crash ping")?;
+
+        let submission_url = ping
+            .submission_url(&self.extra)
+            .context("failed to generate ping submission URL")?;
+
+        let target_file = self
+            .config
+            .ping_dir
+            .as_ref()
+            .unwrap()
+            .join(format!("{}.json", ping.id()));
+
+        let file = std::fs::File::create(&target_file).with_context(|| {
+            format!(
+                "failed to open ping file {} for writing",
+                target_file.display()
+            )
+        })?;
+
+        serde_json::to_writer(file, &ping).context("failed to serialize telemetry crash ping")?;
+
+        let pingsender_path = self.config.sibling_program_path("pingsender");
+
+        crate::process::background_command(&pingsender_path)
+            .arg(submission_url)
+            .arg(target_file)
+            .spawn()
+            .with_context(|| {
+                format!(
+                    "failed to launch pingsender process at {}",
+                    pingsender_path.display()
+                )
+            })?;
+
+        // TODO asynchronously get pingsender result and log it?
+
+        Ok(Some(ping.id().clone()))
+    }
+
+    /// Remove unneeded entries from the extra file, and add some that indicate from where the data
+    /// is being sent.
+    fn sanitize_extra(&mut self) {
+        if let Some(map) = self.extra.as_object_mut() {
+            // Remove these entries, they don't need to be sent.
+            map.remove("ServerURL");
+            map.remove("StackTraces");
+        }
+
+        self.extra["SubmittedFrom"] = "Client".into();
+        self.extra["Throttleable"] = "1".into();
+    }
+
+    /// Update the events file with information about the crash ping, minidump hash, and
+    /// stacktraces.
+    fn update_events_file(
+        &self,
+        minidump_hash: Option<&str>,
+        ping_uuid: Option<Uuid>,
+    ) -> anyhow::Result<()> {
+        use crate::std::io::{BufRead, Error, ErrorKind, Write};
+        struct EventsFile {
+            event_version: String,
+            time: String,
+            uuid: String,
+            pub data: serde_json::Value,
+        }
+
+        impl EventsFile {
+            pub fn parse(mut reader: impl BufRead) -> std::io::Result<Self> {
+                let mut lines = (&mut reader).lines();
+
+                let mut read_field = move |name: &str| -> std::io::Result<String> {
+                    lines.next().transpose()?.ok_or_else(|| {
+                        Error::new(ErrorKind::InvalidData, format!("missing {name} field"))
+                    })
+                };
+
+                let event_version = read_field("event version")?;
+                let time = read_field("time")?;
+                let uuid = read_field("uuid")?;
+                let data = serde_json::from_reader(reader)?;
+                Ok(EventsFile {
+                    event_version,
+                    time,
+                    uuid,
+                    data,
+                })
+            }
+
+            pub fn write(&self, mut writer: impl Write) -> std::io::Result<()> {
+                writeln!(writer, "{}", self.event_version)?;
+                writeln!(writer, "{}", self.time)?;
+                writeln!(writer, "{}", self.uuid)?;
+                serde_json::to_writer(writer, &self.data)?;
+                Ok(())
+            }
+        }
+
+        let Some(events_dir) = &self.config.events_dir else {
+            log::warn!("not updating the events file; no events directory configured");
+            return Ok(());
+        };
+
+        let event_path = events_dir.join(self.config.local_dump_id().as_ref());
+
+        // Read events file.
+        let file = std::fs::File::open(&event_path)
+            .with_context(|| format!("failed to open event file at {}", event_path.display()))?;
+
+        let mut events_file =
+            EventsFile::parse(std::io::BufReader::new(file)).with_context(|| {
+                format!(
+                    "failed to parse events file contents in {}",
+                    event_path.display()
+                )
+            })?;
+
+        // Update events file fields.
+        if let Some(hash) = minidump_hash {
+            events_file.data["MinidumpSha256Hash"] = hash.into();
+        }
+        if let Some(uuid) = ping_uuid {
+            events_file.data["CrashPingUUID"] = uuid.to_string().into();
+        }
+        events_file.data["StackTraces"] = self.extra["StackTraces"].clone();
+
+        // Write altered events file.
+        let file = std::fs::File::create(&event_path).with_context(|| {
+            format!("failed to truncate event file at {}", event_path.display())
+        })?;
+
+        events_file
+            .write(file)
+            .with_context(|| format!("failed to write event file at {}", event_path.display()))
+    }
+
+    /// Check whether the version of the software that generated the crash is EOL.
+    fn check_eol_version(&self) -> anyhow::Result<()> {
+        if let Some(version) = self.extra["Version"].as_str() {
+            if self.config.version_eol_file(version).exists() {
+                self.config.delete_files();
+                anyhow::bail!(self.config.string("crashreporter-error-version-eol"));
+            }
+        }
+        Ok(())
+    }
+
+    /// Save the current settings.
+    fn save_settings(&self) {
+        let result: anyhow::Result<()> = (|| {
+            Ok(self
+                .settings
+                .borrow()
+                .to_writer(std::fs::File::create(&self.settings_file)?)?)
+        })();
+        if let Err(e) = result {
+            log::error!("error while saving settings: {e}");
+        }
+    }
+
+    /// Handle a response from submitting a crash report.
+    ///
+    /// Returns the crash ID to use for the recorded submission event. Errors in this function may
+    /// result in None being returned to consider the crash report submission as a failure even
+    /// though the server did provide a response.
+    fn handle_crash_report_response(
+        &self,
+        response: net::report::Response,
+    ) -> anyhow::Result<Option<String>> {
+        if let Some(version) = response.stop_sending_reports_for {
+            // Create the EOL version file. The content seemingly doesn't matter, but we mimic what
+            // was written by the old crash reporter.
+            if let Err(e) = std::fs::write(self.config.version_eol_file(&version), "1\n") {
+                log::warn!("failed to write EOL file: {e}");
+            }
+        }
+
+        if response.discarded {
+            log::debug!("response indicated that the report was discarded");
+            return Ok(None);
+        }
+
+        let Some(crash_id) = response.crash_id else {
+            log::debug!("response did not provide a crash id");
+            return Ok(None);
+        };
+
+        // Write the id to the `submitted` directory
+        let submitted_dir = self.config.submitted_crash_dir();
+        std::fs::create_dir_all(&submitted_dir).with_context(|| {
+            format!(
+                "failed to create submitted crash directory {}",
+                submitted_dir.display()
+            )
+        })?;
+
+        let crash_id_file = submitted_dir.join(format!("{crash_id}.txt"));
+
+        let mut file = std::fs::File::create(&crash_id_file).with_context(|| {
+            format!(
+                "failed to create submitted crash file for {crash_id} ({})",
+                crash_id_file.display()
+            )
+        })?;
+
+        // Shadow `std::fmt::Write` to use the correct trait below.
+        use crate::std::io::Write;
+
+        if let Err(e) = writeln!(
+            &mut file,
+            "{}",
+            self.config
+                .build_string("crashreporter-crash-identifier")
+                .arg("id", &crash_id)
+                .get()
+        ) {
+            log::warn!(
+                "failed to write to submitted crash file ({}) for {crash_id}: {e}",
+                crash_id_file.display()
+            );
+        }
+
+        if let Some(url) = response.view_url {
+            if let Err(e) = writeln!(
+                &mut file,
+                "{}",
+                self.config
+                    .build_string("crashreporter-crash-details")
+                    .arg("url", url)
+                    .get()
+            ) {
+                log::warn!(
+                    "failed to write view url to submitted crash file ({}) for {crash_id}: {e}",
+                    crash_id_file.display()
+                );
+            }
+        }
+
+        Ok(Some(crash_id))
+    }
+
+    /// Write the submission event.
+    ///
+    /// A `None` crash_id indicates that the submission failed.
+    fn write_submission_event(&self, crash_id: Option<String>) -> anyhow::Result<()> {
+        let Some(events_dir) = &self.config.events_dir else {
+            // If there's no events dir, don't do anything.
+            return Ok(());
+        };
+
+        let local_id = self.config.local_dump_id();
+        let event_path = events_dir.join(format!("{local_id}-submission"));
+
+        let unix_epoch_seconds = std::time::SystemTime::now()
+            .duration_since(std::time::SystemTime::UNIX_EPOCH)
+            .expect("system time is before the unix epoch")
+            .as_secs();
+        std::fs::write(
+            &event_path,
+            format!(
+                "crash.submission.1\n{unix_epoch_seconds}\n{local_id}\n{}\n{}",
+                crash_id.is_some(),
+                crash_id.as_deref().unwrap_or("")
+            ),
+        )
+        .with_context(|| format!("failed to write event to {}", event_path.display()))
+    }
+
+    /// Restart the program.
+    fn restart_process(&self) {
+        if self.config.restart_command.is_none() {
+            // The restart button should be hidden in this case, so this error should not occur.
+            log::error!("no process configured for restart");
+            return;
+        }
+
+        let mut cmd = Command::new(self.config.restart_command.as_ref().unwrap());
+        cmd.args(&self.config.restart_args)
+            .stdin(std::process::Stdio::null())
+            .stdout(std::process::Stdio::null())
+            .stderr(std::process::Stdio::null());
+        if let Some(xul_app_file) = &self.config.app_file {
+            cmd.env("XUL_APP_FILE", xul_app_file);
+        }
+        log::debug!("restarting process: {:?}", cmd);
+        if let Err(e) = cmd.spawn() {
+            log::error!("failed to restart process: {e}");
+        }
+    }
+
+    /// Run the crash reporting UI.
+    fn run_ui(&mut self) {
+        use crate::std::{sync::mpsc, thread};
+
+        let (logic_send, logic_recv) = mpsc::channel();
+        // Wrap work_send in an Arc so that it can be captured weakly by the work queue and
+        // drop when the UI finishes, including panics (allowing the logic thread to exit).
+        //
+        // We need to wrap in a Mutex because std::mpsc::Sender isn't Sync (until rust 1.72).
+        let logic_send = Arc::new(Mutex::new(logic_send));
+
+        let weak_logic_send = Arc::downgrade(&logic_send);
+        let logic_remote_queue = AsyncTask::new(move |f| {
+            if let Some(logic_send) = weak_logic_send.upgrade() {
+                // This is best-effort: ignore errors.
+                let _ = logic_send.lock().unwrap().send(f);
+            }
+        });
+
+        let crash_ui = ReportCrashUI::new(
+            &*self.settings.borrow(),
+            self.config.clone(),
+            logic_remote_queue,
+        );
+
+        // Set the UI remote queue.
+        self.ui = Some(crash_ui.async_task());
+
+        // Spawn a separate thread to handle all interactions with `self`. This prevents blocking
+        // the UI for any reason.
+
+        // Use a barrier to ensure both threads are live before either starts (ensuring they
+        // can immediately queue work for each other).
+        let barrier = std::sync::Barrier::new(2);
+        let barrier = &barrier;
+        thread::scope(move |s| {
+            // Move `logic_send` into this scope so that it will drop when the scope completes
+            // (which will drop the `mpsc::Sender` and cause the logic thread to complete and join
+            // when the UI finishes so the scope can exit).
+            let _logic_send = logic_send;
+            s.spawn(move || {
+                barrier.wait();
+                while let Ok(f) = logic_recv.recv() {
+                    f(self);
+                }
+                // Clear the UI remote queue, using it after this point is an error.
+                //
+                // NOTE we do this here because the compiler can't reason about `self` being safely
+                // accessible after `thread::scope` returns. This is effectively the same result
+                // since the above loop will only exit when `logic_send` is dropped at the end of
+                // the scope.
+                self.ui = None;
+            });
+
+            barrier.wait();
+            crash_ui.run()
+        });
+    }
+}
+
+// These methods may interact with `self.ui`.
+impl ReportCrash {
+    /// Update the submission details shown in the UI.
+    pub fn update_details(&self) {
+        use crate::std::fmt::Write;
+
+        let extra = self.current_extra_data();
+
+        let mut details = String::new();
+        let mut entries: Vec<_> = extra.as_object().unwrap().into_iter().collect();
+        entries.sort_unstable_by_key(|(k, _)| *k);
+        for (key, value) in entries {
+            let _ = write!(details, "{key}: ");
+            if let Some(v) = value.as_str() {
+                details.push_str(v);
+            } else {
+                match serde_json::to_string(value) {
+                    Ok(s) => details.push_str(&s),
+                    Err(e) => {
+                        let _ = write!(details, "<serialization error: {e}>");
+                    }
+                }
+            }
+            let _ = writeln!(details);
+        }
+        let _ = writeln!(
+            details,
+            "{}",
+            self.config.string("crashreporter-report-info")
+        );
+
+        self.ui().push(move |ui| *ui.details.borrow_mut() = details);
+    }
+
+    /// Restart the application and send the crash report.
+    pub fn restart(&self) {
+        self.save_settings();
+        // Get the program restarted before sending the report.
+        self.restart_process();
+        let result = self.try_send();
+        self.close_window(result.is_some());
+    }
+
+    /// Quit and send the crash report.
+    pub fn quit(&self) {
+        self.save_settings();
+        let result = self.try_send();
+        self.close_window(result.is_some());
+    }
+
+    fn close_window(&self, report_sent: bool) {
+        if report_sent && !self.config.auto_submit && !cfg!(test) {
+            // Add a delay to allow the user to see the result.
+            std::thread::sleep(std::time::Duration::from_secs(5));
+        }
+
+        self.ui().push(|r| r.close_window.fire(&()));
+    }
+
+    /// Try to send the report.
+    ///
+    /// This function may be called without a UI active (if auto_submit is true), so it will not
+    /// panic if `self.ui` is unset.
+    ///
+    /// Returns whether the report was received (regardless of whether the response was processed
+    /// successfully), if a report could be sent at all (based on the configuration).
+    fn try_send(&self) -> Option<bool> {
+        self.attempted_to_send.store(true, Relaxed);
+        let send_report = self.settings.borrow().submit_report;
+
+        if !send_report {
+            log::trace!("not sending report due to user setting");
+            return None;
+        }
+
+        // TODO? load proxy info from libgconf on linux
+
+        let Some(url) = &self.config.report_url else {
+            log::warn!("not sending report due to missing report url");
+            return None;
+        };
+
+        if let Some(ui) = &self.ui {
+            ui.push(|r| *r.submit_state.borrow_mut() = SubmitState::InProgress);
+        }
+
+        // Send the report to the server.
+        let extra = self.current_extra_data();
+        let memory_file = self.config.memory_file();
+        let report = net::report::CrashReport {
+            extra: &extra,
+            dump_file: self.config.dump_file(),
+            memory_file: memory_file.as_deref(),
+            url,
+        };
+
+        let report_response = report
+            .send()
+            .map(Some)
+            .unwrap_or_else(|e| {
+                log::error!("failed to initialize report transmission: {e}");
+                None
+            })
+            .and_then(|sender| {
+                // Normally we might want to do the following asynchronously since it will block,
+                // however we don't really need the Logic thread to do anything else (the UI
+                // becomes disabled from this point onward), so we just do it here. Same goes for
+                // the `std::thread::sleep` in close_window() later on.
+                sender.finish().map(Some).unwrap_or_else(|e| {
+                    log::error!("failed to send report: {e}");
+                    None
+                })
+            });
+
+        let report_received = report_response.is_some();
+        let crash_id = report_response.and_then(|response| {
+            self.handle_crash_report_response(response)
+                .unwrap_or_else(|e| {
+                    log::error!("failed to handle crash report response: {e}");
+                    None
+                })
+        });
+
+        if report_received {
+            // If the response could be handled (indicated by the returned crash id), clean up by
+            // deleting the minidump files. Otherwise, prune old minidump files.
+            if crash_id.is_some() {
+                self.config.delete_files();
+            } else {
+                if let Err(e) = self.config.prune_files() {
+                    log::warn!("failed to prune files: {e}");
+                }
+            }
+        }
+
+        if let Err(e) = self.write_submission_event(crash_id) {
+            log::warn!("failed to write submission event: {e}");
+        }
+
+        // Indicate whether the report was sent successfully, regardless of whether the response
+        // was processed successfully.
+        //
+        // FIXME: this is how the old crash reporter worked, but we might want to change this
+        // behavior.
+        if let Some(ui) = &self.ui {
+            ui.push(move |r| {
+                *r.submit_state.borrow_mut() = if report_received {
+                    SubmitState::Success
+                } else {
+                    SubmitState::Failure
+                }
+            });
+        }
+
+        Some(report_received)
+    }
+
+    /// Form the extra data, taking into account user input.
+    fn current_extra_data(&self) -> serde_json::Value {
+        let include_address = self.settings.borrow().include_url;
+        let comment = if !self.config.auto_submit {
+            self.ui().wait(|r| r.comment.get())
+        } else {
+            Default::default()
+        };
+
+        let mut extra = self.extra.clone();
+
+        if !comment.is_empty() {
+            extra["Comments"] = comment.into();
+        }
+
+        if !include_address {
+            extra.as_object_mut().unwrap().remove("URL");
+        }
+
+        extra
+    }
+
+    fn ui(&self) -> &AsyncTask<ReportCrashUIState> {
+        self.ui.as_ref().expect("UI remote queue missing")
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/main.rs b/toolkit/crashreporter/client/app/src/main.rs
new file mode 100644
index 0000000000..07e1b04cb8
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/main.rs
@@ -0,0 +1,229 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+//! The crash reporter application.
+//!
+//! # Architecture
+//! The application uses a simple declarative [UI model](ui::model) to define the UI. This model
+//! contains [data bindings](data) which provide the dynamic behaviors of the UI. Separate UI
+//! implementations for linux (gtk), macos (cocoa), and windows (win32) exist, as well as a test UI
+//! which is virtual (no actual interface is presented) but allows runtime introspection.
+//!
+//! # Mocking
+//! This application contains mock interfaces for all the `std` functions it uses which interact
+//! with the host system. You can see their implementation in [`crate::std`]. To enable mocking,
+//! use the `mock` feature or build with `MOZ_CRASHREPORTER_MOCK` set (which, in `build.rs`, is
+//! translated to a `cfg` option). *Note* that this cfg _must_ be enabled when running tests.
+//! Unfortunately it is not possible to detect whether tests are being built in `build.rs, which
+//! is why a feature needed to be made in the first place (it is enabled automatically when running
+//! `mach rusttests`).
+//!
+//! Currently the input program configuration which is mocked when running the application is fixed
+//! (see the [`main`] implementation in this file). If needed in the future, it would be nice to
+//! extend this to allow runtime tweaking.
+//!
+//! # Development
+//! Because of the mocking support previously mentioned, in generally any `std` imports should
+//! actually use `crate::std`. If mocked functions/types are missing, they should be added with
+//! appropriate mocking hooks.
+
+// Use the WINDOWS windows subsystem. This prevents a console window from opening with the
+// application.
+#![cfg_attr(windows, windows_subsystem = "windows")]
+
+use crate::std::sync::Arc;
+use anyhow::Context;
+use config::Config;
+
+/// cc is short for Clone Capture, a shorthand way to clone a bunch of values before an expression
+/// (particularly useful for closures).
+///
+/// It is defined here to allow it to be used in all submodules (textual scope lookup).
+macro_rules! cc {
+    ( ($($c:ident),*) $e:expr ) => {
+        {
+            $(let $c = $c.clone();)*
+            $e
+        }
+    }
+}
+
+mod async_task;
+mod config;
+mod data;
+mod lang;
+mod logging;
+mod logic;
+mod net;
+mod process;
+mod settings;
+mod std;
+mod thread_bound;
+mod ui;
+
+#[cfg(test)]
+mod test;
+
+#[cfg(not(mock))]
+fn main() {
+    let log_target = logging::init();
+
+    let mut config = Config::new();
+    let config_result = config.read_from_environment();
+    config.log_target = Some(log_target);
+
+    let mut config = Arc::new(config);
+
+    let result = config_result.and_then(|()| {
+        let attempted_send = try_run(&mut config)?;
+        if !attempted_send {
+            // Exited without attempting to send the crash report; delete files.
+            config.delete_files();
+        }
+        Ok(())
+    });
+
+    if let Err(message) = result {
+        // TODO maybe errors should also delete files?
+        log::error!("exiting with error: {message}");
+        if !config.auto_submit {
+            // Only show a dialog if auto_submit is disabled.
+            ui::error_dialog(&config, message);
+        }
+        std::process::exit(1);
+    }
+}
+
+#[cfg(mock)]
+fn main() {
+    // TODO it'd be nice to be able to set these values at runtime in some way when running the
+    // mock application.
+
+    use crate::std::{
+        fs::{MockFS, MockFiles},
+        mock,
+        process::Command,
+    };
+    const MOCK_MINIDUMP_EXTRA: &str = r#"{
+                            "Vendor": "FooCorp",
+                            "ProductName": "Bar",
+                            "ReleaseChannel": "release",
+                            "BuildID": "1234",
+                            "StackTraces": {
+                                "status": "OK"
+                            },
+                            "Version": "100.0",
+                            "ServerURL": "https://reports.example",
+                            "TelemetryServerURL": "https://telemetry.example",
+                            "TelemetryClientId": "telemetry_client",
+                            "TelemetrySessionId": "telemetry_session",
+                            "URL": "https://url.example"
+                        }"#;
+
+    // Actual content doesn't matter, aside from the hash that is generated.
+    const MOCK_MINIDUMP_FILE: &[u8] = &[1, 2, 3, 4];
+    const MOCK_CURRENT_TIME: &str = "2004-11-09T12:34:56Z";
+    const MOCK_PING_UUID: uuid::Uuid = uuid::Uuid::nil();
+    const MOCK_REMOTE_CRASH_ID: &str = "8cbb847c-def2-4f68-be9e-000000000000";
+
+    // Create a default set of files which allow successful operation.
+    let mock_files = MockFiles::new();
+    mock_files
+        .add_file("minidump.dmp", MOCK_MINIDUMP_FILE)
+        .add_file("minidump.extra", MOCK_MINIDUMP_EXTRA);
+
+    // Create a default mock environment which allows successful operation.
+    let mut mock = mock::builder();
+    mock.set(
+        Command::mock("work_dir/minidump-analyzer"),
+        Box::new(|_| Ok(crate::std::process::success_output())),
+    )
+    .set(
+        Command::mock("work_dir/pingsender"),
+        Box::new(|_| Ok(crate::std::process::success_output())),
+    )
+    .set(
+        Command::mock("curl"),
+        Box::new(|_| {
+            let mut output = crate::std::process::success_output();
+            output.stdout = format!("CrashID={MOCK_REMOTE_CRASH_ID}").into();
+            // Network latency.
+            std::thread::sleep(std::time::Duration::from_secs(2));
+            Ok(output)
+        }),
+    )
+    .set(MockFS, mock_files.clone())
+    .set(
+        crate::std::env::MockCurrentExe,
+        "work_dir/crashreporter".into(),
+    )
+    .set(
+        crate::std::time::MockCurrentTime,
+        time::OffsetDateTime::parse(
+            MOCK_CURRENT_TIME,
+            &time::format_description::well_known::Rfc3339,
+        )
+        .unwrap()
+        .into(),
+    )
+    .set(mock::MockHook::new("ping_uuid"), MOCK_PING_UUID);
+
+    let result = mock.run(|| {
+        let mut cfg = Config::new();
+        cfg.data_dir = Some("data_dir".into());
+        cfg.events_dir = Some("events_dir".into());
+        cfg.ping_dir = Some("ping_dir".into());
+        cfg.dump_file = Some("minidump.dmp".into());
+        cfg.restart_command = Some("mockfox".into());
+        cfg.strings = Some(lang::load().unwrap());
+        let mut cfg = Arc::new(cfg);
+        try_run(&mut cfg)
+    });
+
+    if let Err(e) = result {
+        log::error!("exiting with error: {e}");
+        std::process::exit(1);
+    }
+}
+
+fn try_run(config: &mut Arc<Config>) -> anyhow::Result<bool> {
+    if config.dump_file.is_none() {
+        if !config.auto_submit {
+            Err(anyhow::anyhow!(config.string("crashreporter-information")))
+        } else {
+            Ok(false)
+        }
+    } else {
+        // Run minidump-analyzer to gather stack traces.
+        {
+            let analyzer_path = config.sibling_program_path("minidump-analyzer");
+            let mut cmd = crate::process::background_command(&analyzer_path);
+            if config.dump_all_threads {
+                cmd.arg("--full");
+            }
+            cmd.arg(config.dump_file());
+            let output = cmd
+                .output()
+                .with_context(|| config.string("crashreporter-error-minidump-analyzer"))?;
+            if !output.status.success() {
+                log::warn!(
+                    "minidump-analyzer failed to run ({});\n\nstderr: {}\n\nstdout: {}",
+                    output.status,
+                    String::from_utf8_lossy(&output.stderr),
+                    String::from_utf8_lossy(&output.stdout),
+                );
+            }
+        }
+
+        let extra = {
+            // Perform a few things which may change the config, then treat is as immutable.
+            let config = Arc::get_mut(config).expect("unexpected config references");
+            let extra = config.load_extra_file()?;
+            config.move_crash_data_to_pending()?;
+            extra
+        };
+
+        logic::ReportCrash::new(config.clone(), extra)?.run()
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/net/legacy_telemetry.rs b/toolkit/crashreporter/client/app/src/net/legacy_telemetry.rs
new file mode 100644
index 0000000000..680f1614b0
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/net/legacy_telemetry.rs
@@ -0,0 +1,177 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Support for legacy telemetry ping creation. The ping support serialization which should be used
+//! when submitting.
+
+use anyhow::Context;
+use serde::Serialize;
+use std::collections::BTreeMap;
+use uuid::Uuid;
+
+const TELEMETRY_VERSION: u64 = 4;
+const PAYLOAD_VERSION: u64 = 1;
+
+// Generated by `build.rs`.
+// static PING_ANNOTATIONS: phf::Set<&'static str>;
+include!(concat!(env!("OUT_DIR"), "/ping_annotations.rs"));
+
+#[derive(Serialize)]
+#[serde(tag = "type", rename_all = "camelCase")]
+pub enum Ping<'a> {
+    Crash {
+        id: Uuid,
+        version: u64,
+        #[serde(with = "time::serde::rfc3339")]
+        creation_date: time::OffsetDateTime,
+        client_id: &'a str,
+        #[serde(skip_serializing_if = "serde_json::Value::is_null")]
+        environment: serde_json::Value,
+        payload: Payload<'a>,
+        application: Application<'a>,
+    },
+}
+
+time::serde::format_description!(date_format, Date, "[year]-[month]-[day]");
+
+#[derive(Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct Payload<'a> {
+    session_id: &'a str,
+    version: u64,
+    #[serde(with = "date_format")]
+    crash_date: time::Date,
+    #[serde(with = "time::serde::rfc3339")]
+    crash_time: time::OffsetDateTime,
+    has_crash_environment: bool,
+    crash_id: &'a str,
+    minidump_sha256_hash: Option<&'a str>,
+    process_type: &'a str,
+    #[serde(skip_serializing_if = "serde_json::Value::is_null")]
+    stack_traces: serde_json::Value,
+    metadata: BTreeMap<&'a str, &'a str>,
+}
+
+#[derive(Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct Application<'a> {
+    vendor: &'a str,
+    name: &'a str,
+    build_id: &'a str,
+    display_version: String,
+    platform_version: String,
+    version: &'a str,
+    channel: &'a str,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    architecture: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    xpcom_abi: Option<String>,
+}
+
+impl<'a> Ping<'a> {
+    pub fn crash(
+        extra: &'a serde_json::Value,
+        crash_id: &'a str,
+        minidump_sha256_hash: Option<&'a str>,
+    ) -> anyhow::Result<Self> {
+        let now: time::OffsetDateTime = crate::std::time::SystemTime::now().into();
+        let environment: serde_json::Value = extra["TelemetryEnvironment"]
+            .as_str()
+            .and_then(|estr| serde_json::from_str(estr).ok())
+            .unwrap_or_default();
+
+        // The subset of extra file entries (crash annotations) which are allowed in pings.
+        let metadata = extra
+            .as_object()
+            .map(|map| {
+                map.iter()
+                    .filter_map(|(k, v)| {
+                        PING_ANNOTATIONS
+                            .contains(k)
+                            .then(|| k.as_str())
+                            .zip(v.as_str())
+                    })
+                    .collect()
+            })
+            .unwrap_or_default();
+
+        let display_version = environment
+            .pointer("/build/displayVersion")
+            .and_then(|s| s.as_str())
+            .unwrap_or_default()
+            .to_owned();
+        let platform_version = environment
+            .pointer("/build/platformVersion")
+            .and_then(|s| s.as_str())
+            .unwrap_or_default()
+            .to_owned();
+        let architecture = environment
+            .pointer("/build/architecture")
+            .and_then(|s| s.as_str())
+            .map(ToOwned::to_owned);
+        let xpcom_abi = environment
+            .pointer("/build/xpcomAbi")
+            .and_then(|s| s.as_str())
+            .map(ToOwned::to_owned);
+
+        Ok(Ping::Crash {
+            id: crate::std::mock::hook(Uuid::new_v4(), "ping_uuid"),
+            version: TELEMETRY_VERSION,
+            creation_date: now,
+            client_id: extra["TelemetryClientId"]
+                .as_str()
+                .context("missing TelemetryClientId")?,
+            environment,
+            payload: Payload {
+                session_id: extra["TelemetrySessionId"]
+                    .as_str()
+                    .context("missing TelemetrySessionId")?,
+                version: PAYLOAD_VERSION,
+                crash_date: now.date(),
+                crash_time: now,
+                has_crash_environment: true,
+                crash_id,
+                minidump_sha256_hash,
+                process_type: "main",
+                stack_traces: extra["StackTraces"].clone(),
+                metadata,
+            },
+            application: Application {
+                vendor: extra["Vendor"].as_str().unwrap_or_default(),
+                name: extra["ProductName"].as_str().unwrap_or_default(),
+                build_id: extra["BuildID"].as_str().unwrap_or_default(),
+                display_version,
+                platform_version,
+                version: extra["Version"].as_str().unwrap_or_default(),
+                channel: extra["ReleaseChannel"].as_str().unwrap_or_default(),
+                architecture,
+                xpcom_abi,
+            },
+        })
+    }
+
+    /// Generate the telemetry URL for submitting this ping.
+    pub fn submission_url(&self, extra: &serde_json::Value) -> anyhow::Result<String> {
+        let url = extra["TelemetryServerURL"]
+            .as_str()
+            .context("missing TelemetryServerURL")?;
+        let id = self.id();
+        let name = extra["ProductName"]
+            .as_str()
+            .context("missing ProductName")?;
+        let version = extra["Version"].as_str().context("missing Version")?;
+        let channel = extra["ReleaseChannel"]
+            .as_str()
+            .context("missing ReleaseChannel")?;
+        let buildid = extra["BuildID"].as_str().context("missing BuildID")?;
+        Ok(format!("{url}/submit/telemetry/{id}/crash/{name}/{version}/{channel}/{buildid}?v={TELEMETRY_VERSION}"))
+    }
+
+    /// Get the ping identifier.
+    pub fn id(&self) -> &Uuid {
+        match self {
+            Ping::Crash { id, .. } => id,
+        }
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/net/libcurl.rs b/toolkit/crashreporter/client/app/src/net/libcurl.rs
new file mode 100644
index 0000000000..0adfd7d4b4
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/net/libcurl.rs
@@ -0,0 +1,406 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+//! Partial libcurl bindings with some wrappers for safe cleanup.
+
+use crate::std::path::Path;
+use libloading::{Library, Symbol};
+use once_cell::sync::Lazy;
+use std::ffi::{c_char, c_long, c_uint, CStr, CString};
+
+// Constants lifted from `curl.h`
+const CURLE_OK: CurlCode = 0;
+const CURL_ERROR_SIZE: usize = 256;
+
+const CURLOPTTYPE_LONG: CurlOption = 0;
+const CURLOPTTYPE_OBJECTPOINT: CurlOption = 10000;
+const CURLOPTTYPE_FUNCTIONPOINT: CurlOption = 20000;
+const CURLOPTTYPE_STRINGPOINT: CurlOption = CURLOPTTYPE_OBJECTPOINT;
+const CURLOPTTYPE_CBPOINT: CurlOption = CURLOPTTYPE_OBJECTPOINT;
+
+const CURLOPT_WRITEDATA: CurlOption = CURLOPTTYPE_CBPOINT + 1;
+const CURLOPT_URL: CurlOption = CURLOPTTYPE_STRINGPOINT + 2;
+const CURLOPT_ERRORBUFFER: CurlOption = CURLOPTTYPE_OBJECTPOINT + 10;
+const CURLOPT_WRITEFUNCTION: CurlOption = CURLOPTTYPE_FUNCTIONPOINT + 11;
+const CURLOPT_USERAGENT: CurlOption = CURLOPTTYPE_STRINGPOINT + 18;
+const CURLOPT_MIMEPOST: CurlOption = CURLOPTTYPE_OBJECTPOINT + 269;
+const CURLOPT_MAXREDIRS: CurlOption = CURLOPTTYPE_LONG + 68;
+
+const CURLINFO_LONG: CurlInfo = 0x200000;
+const CURLINFO_RESPONSE_CODE: CurlInfo = CURLINFO_LONG + 2;
+
+const CURL_LIB_NAMES: &[&str] = if cfg!(target_os = "linux") {
+    &[
+        "libcurl.so",
+        "libcurl.so.4",
+        // Debian gives libcurl a different name when it is built against GnuTLS
+        "libcurl-gnutls.so",
+        "libcurl-gnutls.so.4",
+        // Older versions in case we find nothing better
+        "libcurl.so.3",
+        "libcurl-gnutls.so.3", // See above for Debian
+    ]
+} else if cfg!(target_os = "macos") {
+    &[
+        "/usr/lib/libcurl.dylib",
+        "/usr/lib/libcurl.4.dylib",
+        "/usr/lib/libcurl.3.dylib",
+    ]
+} else if cfg!(target_os = "windows") {
+    &["libcurl.dll", "curl.dll"]
+} else {
+    &[]
+};
+
+// Shim until min rust version 1.74 which allows std::io::Error::other
+fn error_other<E>(error: E) -> std::io::Error
+where
+    E: Into<Box<dyn std::error::Error + Send + Sync>>,
+{
+    std::io::Error::new(std::io::ErrorKind::Other, error)
+}
+
+#[repr(transparent)]
+#[derive(Clone, Copy)]
+struct CurlHandle(*mut ());
+type CurlCode = c_uint;
+type CurlOption = c_uint;
+type CurlInfo = c_uint;
+#[repr(transparent)]
+#[derive(Clone, Copy)]
+struct CurlMime(*mut ());
+#[repr(transparent)]
+#[derive(Clone, Copy)]
+struct CurlMimePart(*mut ());
+
+macro_rules! library_binding {
+    ( $localname:ident members[$($members:tt)*] load[$($load:tt)*] fn $name:ident $args:tt $( -> $ret:ty )? ; $($rest:tt)* ) => {
+        library_binding! {
+            $localname
+            members[
+                $($members)*
+                $name: Symbol<'static, unsafe extern fn $args $(->$ret)?>,
+            ]
+            load[
+                $($load)*
+                $name: unsafe {
+                    let symbol = $localname.get::<unsafe extern fn $args $(->$ret)?>(stringify!($name).as_bytes())
+                    .map_err(|e| std::io::Error::new(std::io::ErrorKind::NotFound, e))?;
+                    // All symbols refer to library, so `'static` lifetimes are safe (`library`
+                    // will outlive them).
+                    std::mem::transmute(symbol)
+                },
+            ]
+            $($rest)*
+        }
+    };
+    ( $localname:ident members[$($members:tt)*] load[$($load:tt)*] ) => {
+        pub struct Curl {
+            $($members)*
+            _library: Library
+        }
+
+        impl Curl {
+            fn load() -> std::io::Result<Self> {
+                // Try each of the libraries, debug-logging load failures.
+                let library = CURL_LIB_NAMES.iter().find_map(|name| {
+                    log::debug!("attempting to load {name}");
+                    match unsafe { Library::new(name) } {
+                        Ok(lib) => {
+                            log::info!("loaded {name}");
+                            Some(lib)
+                        }
+                        Err(e) => {
+                            log::debug!("error when loading {name}: {e}");
+                            None
+                        }
+                    }
+                });
+
+                let $localname = library.ok_or_else(|| {
+                    std::io::Error::new(std::io::ErrorKind::NotFound, "failed to find curl library")
+                })?;
+
+                Ok(Curl { $($load)* _library: $localname })
+            }
+        }
+    };
+    ( $($rest:tt)* ) => {
+        library_binding! {
+            library members[] load[] $($rest)*
+        }
+    }
+}
+
+library_binding! {
+    fn curl_easy_init() -> CurlHandle;
+    fn curl_easy_setopt(CurlHandle, CurlOption, ...) -> CurlCode;
+    fn curl_easy_perform(CurlHandle) -> CurlCode;
+    fn curl_easy_getinfo(CurlHandle, CurlInfo, ...) -> CurlCode;
+    fn curl_easy_cleanup(CurlHandle);
+    fn curl_mime_init(CurlHandle) -> CurlMime;
+    fn curl_mime_addpart(CurlMime) -> CurlMimePart;
+    fn curl_mime_name(CurlMimePart, *const c_char) -> CurlCode;
+    fn curl_mime_filename(CurlMimePart, *const c_char) -> CurlCode;
+    fn curl_mime_type(CurlMimePart, *const c_char) -> CurlCode;
+    fn curl_mime_data(CurlMimePart, *const c_char, usize) -> CurlCode;
+    fn curl_mime_filedata(CurlMimePart, *const c_char) -> CurlCode;
+    fn curl_mime_free(CurlMime);
+}
+
+/// Load libcurl if possible.
+pub fn load() -> std::io::Result<&'static Curl> {
+    static CURL: Lazy<std::io::Result<Curl>> = Lazy::new(Curl::load);
+    CURL.as_ref().map_err(error_other)
+}
+
+#[derive(Debug)]
+pub struct Error {
+    code: CurlCode,
+    error: Option<String>,
+}
+
+impl std::fmt::Display for Error {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        write!(f, "curl error code {}", self.code)?;
+        if let Some(e) = &self.error {
+            write!(f, ": {e}")?;
+        }
+        Ok(())
+    }
+}
+
+impl std::error::Error for Error {}
+
+impl From<Error> for std::io::Error {
+    fn from(e: Error) -> Self {
+        error_other(e)
+    }
+}
+
+pub type Result<T> = std::result::Result<T, Error>;
+
+fn to_result(code: CurlCode) -> Result<()> {
+    if code == CURLE_OK {
+        Ok(())
+    } else {
+        Err(Error { code, error: None })
+    }
+}
+
+impl Curl {
+    pub fn easy(&self) -> std::io::Result<Easy> {
+        let handle = unsafe { (self.curl_easy_init)() };
+        if handle.0.is_null() {
+            Err(error_other("curl_easy_init failed"))
+        } else {
+            Ok(Easy {
+                lib: self,
+                handle,
+                mime: Default::default(),
+            })
+        }
+    }
+}
+
+struct ErrorBuffer([u8; CURL_ERROR_SIZE]);
+
+impl Default for ErrorBuffer {
+    fn default() -> Self {
+        ErrorBuffer([0; CURL_ERROR_SIZE])
+    }
+}
+
+pub struct Easy<'a> {
+    lib: &'a Curl,
+    handle: CurlHandle,
+    mime: Option<Mime<'a>>,
+}
+
+impl<'a> Easy<'a> {
+    pub fn set_url(&mut self, url: &str) -> Result<()> {
+        let url = CString::new(url.to_string()).unwrap();
+        to_result(unsafe { (self.lib.curl_easy_setopt)(self.handle, CURLOPT_URL, url.as_ptr()) })
+    }
+
+    pub fn set_user_agent(&mut self, user_agent: &str) -> Result<()> {
+        let ua = CString::new(user_agent.to_string()).unwrap();
+        to_result(unsafe {
+            (self.lib.curl_easy_setopt)(self.handle, CURLOPT_USERAGENT, ua.as_ptr())
+        })
+    }
+
+    pub fn mime(&self) -> std::io::Result<Mime<'a>> {
+        let handle = unsafe { (self.lib.curl_mime_init)(self.handle) };
+        if handle.0.is_null() {
+            Err(error_other("curl_mime_init failed"))
+        } else {
+            Ok(Mime {
+                lib: self.lib,
+                handle,
+            })
+        }
+    }
+
+    pub fn set_mime_post(&mut self, mime: Mime<'a>) -> Result<()> {
+        let result = to_result(unsafe {
+            (self.lib.curl_easy_setopt)(self.handle, CURLOPT_MIMEPOST, mime.handle)
+        });
+        if result.is_ok() {
+            self.mime = Some(mime);
+        }
+        result
+    }
+
+    pub fn set_max_redirs(&mut self, redirs: c_long) -> Result<()> {
+        to_result(unsafe { (self.lib.curl_easy_setopt)(self.handle, CURLOPT_MAXREDIRS, redirs) })
+    }
+
+    /// Returns the response data on success.
+    pub fn perform(&self) -> Result<Vec<u8>> {
+        // Set error buffer, but degrade service if it doesn't work.
+        let mut error_buffer = ErrorBuffer::default();
+        let error_buffer_set = unsafe {
+            (self.lib.curl_easy_setopt)(
+                self.handle,
+                CURLOPT_ERRORBUFFER,
+                error_buffer.0.as_mut_ptr() as *mut c_char,
+            )
+        } == CURLE_OK;
+
+        // Set the write function to fill a Vec. If there is a panic, this might leave stale
+        // pointers in the curl options, but they won't be used without another perform, at which
+        // point they'll be overwritten.
+        let mut data: Vec<u8> = Vec::new();
+        extern "C" fn write_callback(
+            data: *const u8,
+            size: usize,
+            nmemb: usize,
+            dest: &mut Vec<u8>,
+        ) -> usize {
+            let total = size * nmemb;
+            dest.extend(unsafe { std::slice::from_raw_parts(data, total) });
+            total
+        }
+        unsafe {
+            to_result((self.lib.curl_easy_setopt)(
+                self.handle,
+                CURLOPT_WRITEFUNCTION,
+                write_callback as extern "C" fn(*const u8, usize, usize, &mut Vec<u8>) -> usize,
+            ))?;
+            to_result((self.lib.curl_easy_setopt)(
+                self.handle,
+                CURLOPT_WRITEDATA,
+                &mut data as *mut _,
+            ))?;
+        };
+
+        let mut result = to_result(unsafe { (self.lib.curl_easy_perform)(self.handle) });
+
+        // Clean up a bit by unsetting the write function and write data, though they won't be used
+        // anywhere else. Ignore return values.
+        unsafe {
+            (self.lib.curl_easy_setopt)(
+                self.handle,
+                CURLOPT_WRITEFUNCTION,
+                std::ptr::null_mut::<()>(),
+            );
+            (self.lib.curl_easy_setopt)(self.handle, CURLOPT_WRITEDATA, std::ptr::null_mut::<()>());
+        }
+
+        if error_buffer_set {
+            unsafe {
+                (self.lib.curl_easy_setopt)(
+                    self.handle,
+                    CURLOPT_ERRORBUFFER,
+                    std::ptr::null_mut::<()>(),
+                )
+            };
+            if let Err(e) = &mut result {
+                if let Ok(cstr) = CStr::from_bytes_until_nul(error_buffer.0.as_slice()) {
+                    e.error = Some(cstr.to_string_lossy().into_owned());
+                }
+            }
+        }
+
+        result.map(move |()| data)
+    }
+
+    pub fn get_response_code(&self) -> Result<u64> {
+        let mut code = c_long::default();
+        to_result(unsafe {
+            (self.lib.curl_easy_getinfo)(
+                self.handle,
+                CURLINFO_RESPONSE_CODE,
+                &mut code as *mut c_long,
+            )
+        })?;
+        Ok(code.try_into().expect("negative http response code"))
+    }
+}
+
+impl Drop for Easy<'_> {
+    fn drop(&mut self) {
+        self.mime.take();
+        unsafe { (self.lib.curl_easy_cleanup)(self.handle) };
+    }
+}
+
+pub struct Mime<'a> {
+    lib: &'a Curl,
+    handle: CurlMime,
+}
+
+impl<'a> Mime<'a> {
+    pub fn add_part(&mut self) -> std::io::Result<MimePart<'a>> {
+        let handle = unsafe { (self.lib.curl_mime_addpart)(self.handle) };
+        if handle.0.is_null() {
+            Err(error_other("curl_mime_addpart failed"))
+        } else {
+            Ok(MimePart {
+                lib: self.lib,
+                handle,
+            })
+        }
+    }
+}
+
+impl Drop for Mime<'_> {
+    fn drop(&mut self) {
+        unsafe { (self.lib.curl_mime_free)(self.handle) };
+    }
+}
+
+pub struct MimePart<'a> {
+    lib: &'a Curl,
+    handle: CurlMimePart,
+}
+
+impl MimePart<'_> {
+    pub fn set_name(&mut self, name: &str) -> Result<()> {
+        let name = CString::new(name.to_string()).unwrap();
+        to_result(unsafe { (self.lib.curl_mime_name)(self.handle, name.as_ptr()) })
+    }
+
+    pub fn set_filename(&mut self, filename: &str) -> Result<()> {
+        let filename = CString::new(filename.to_string()).unwrap();
+        to_result(unsafe { (self.lib.curl_mime_filename)(self.handle, filename.as_ptr()) })
+    }
+
+    pub fn set_type(&mut self, mime_type: &str) -> Result<()> {
+        let mime_type = CString::new(mime_type.to_string()).unwrap();
+        to_result(unsafe { (self.lib.curl_mime_type)(self.handle, mime_type.as_ptr()) })
+    }
+
+    pub fn set_filedata(&mut self, file: &Path) -> Result<()> {
+        let file = CString::new(file.display().to_string()).unwrap();
+        to_result(unsafe { (self.lib.curl_mime_filedata)(self.handle, file.as_ptr()) })
+    }
+
+    pub fn set_data(&mut self, data: &[u8]) -> Result<()> {
+        to_result(unsafe {
+            (self.lib.curl_mime_data)(self.handle, data.as_ptr() as *const c_char, data.len())
+        })
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/net/mod.rs b/toolkit/crashreporter/client/app/src/net/mod.rs
new file mode 100644
index 0000000000..d9951d7fc3
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/net/mod.rs
@@ -0,0 +1,12 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+pub mod legacy_telemetry;
+mod libcurl;
+pub mod report;
+
+#[cfg(test)]
+pub fn can_load_libcurl() -> bool {
+    libcurl::load().is_ok()
+}
diff --git a/toolkit/crashreporter/client/app/src/net/report.rs b/toolkit/crashreporter/client/app/src/net/report.rs
new file mode 100644
index 0000000000..46be952547
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/net/report.rs
@@ -0,0 +1,276 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+//! Support for crash report creation and upload.
+//!
+//! Upload currently uses the system libcurl or curl binary rather than a rust network stack (as
+//! curl is more mature, albeit the code to interact with it must be a bit more careful).
+
+use crate::std::{ffi::OsStr, path::Path, process::Child};
+use anyhow::Context;
+
+#[cfg(mock)]
+use crate::std::mock::{mock_key, MockKey};
+
+#[cfg(mock)]
+mock_key! {
+    pub struct MockLibCurl => Box<dyn Fn(&CrashReport) -> std::io::Result<std::io::Result<String>> + Send + Sync>
+}
+
+pub const USER_AGENT: &str = concat!(env!("CARGO_PKG_NAME"), "/", env!("CARGO_PKG_VERSION"));
+
+/// A crash report to upload.
+///
+/// Post a multipart form payload to the report URL.
+///
+/// The form data contains:
+/// | name | filename | content | mime |
+/// ====================================
+/// | `extra` | `extra.json` | extra json object | `application/json`|
+/// | `upload_file_minidump` | dump file name | dump file contents | derived (probably application/binary) |
+/// if present:
+/// | `memory_report` | memory file name | memory file contents | derived (probably gzipped json) |
+pub struct CrashReport<'a> {
+    pub extra: &'a serde_json::Value,
+    pub dump_file: &'a Path,
+    pub memory_file: Option<&'a Path>,
+    pub url: &'a OsStr,
+}
+
+impl CrashReport<'_> {
+    /// Send the crash report.
+    pub fn send(&self) -> std::io::Result<CrashReportSender> {
+        // Windows 10+ and macOS 10.15+ contain `curl` 7.64.1+ as a system-provided binary, so
+        // `send_with_curl_binary` should not fail.
+        //
+        // Linux distros generally do not contain `curl`, but `libcurl` is very likely to be
+        // incidentally installed (if not outright part of the distro base packages). Based on a
+        // cursory look at the debian repositories as an examplar, the curl binary is much less
+        // likely to be incidentally installed.
+        //
+        // For uniformity, we always will try the curl binary first, then try libcurl if that
+        // fails.
+
+        let extra_json_data = serde_json::to_string(self.extra)?;
+
+        self.send_with_curl_binary(extra_json_data.clone())
+            .or_else(|e| {
+                log::info!("failed to invoke curl ({e}), trying libcurl");
+                self.send_with_libcurl(extra_json_data.clone())
+            })
+    }
+
+    /// Send the crash report using the `curl` binary.
+    fn send_with_curl_binary(&self, extra_json_data: String) -> std::io::Result<CrashReportSender> {
+        let mut cmd = crate::process::background_command("curl");
+
+        cmd.args(["--user-agent", USER_AGENT]);
+
+        cmd.arg("--form");
+        // `@-` causes the data to be read from stdin, which is desirable to not have to worry
+        // about process argument string length limitations (though they are generally pretty high
+        // limits).
+        cmd.arg("extra=@-;filename=extra.json;type=application/json");
+
+        cmd.arg("--form");
+        cmd.arg(format!(
+            "upload_file_minidump=@{}",
+            CurlQuote(&self.dump_file.display().to_string())
+        ));
+
+        if let Some(path) = self.memory_file {
+            cmd.arg("--form");
+            cmd.arg(format!(
+                "memory_report=@{}",
+                CurlQuote(&path.display().to_string())
+            ));
+        }
+
+        cmd.arg(self.url);
+
+        cmd.stdin(std::process::Stdio::piped());
+        cmd.stdout(std::process::Stdio::piped());
+        cmd.stderr(std::process::Stdio::piped());
+
+        cmd.spawn().map(move |child| CrashReportSender::CurlChild {
+            child,
+            extra_json_data,
+        })
+    }
+
+    /// Send the crash report using the `curl` library.
+    fn send_with_libcurl(&self, extra_json_data: String) -> std::io::Result<CrashReportSender> {
+        #[cfg(mock)]
+        if !crate::std::mock::try_hook(false, "use_system_libcurl") {
+            return self.send_with_mock_libcurl(extra_json_data);
+        }
+
+        let curl = super::libcurl::load()?;
+        let mut easy = curl.easy()?;
+
+        easy.set_url(&self.url.to_string_lossy())?;
+        easy.set_user_agent(USER_AGENT)?;
+        easy.set_max_redirs(30)?;
+
+        let mut mime = easy.mime()?;
+        {
+            let mut part = mime.add_part()?;
+            part.set_name("extra")?;
+            part.set_filename("extra.json")?;
+            part.set_type("application/json")?;
+            part.set_data(extra_json_data.as_bytes())?;
+        }
+        {
+            let mut part = mime.add_part()?;
+            part.set_name("upload_file_minidump")?;
+            part.set_filename(&self.dump_file.display().to_string())?;
+            part.set_filedata(self.dump_file)?;
+        }
+        if let Some(path) = self.memory_file {
+            let mut part = mime.add_part()?;
+            part.set_name("memory_report")?;
+            part.set_filename(&path.display().to_string())?;
+            part.set_filedata(path)?;
+        }
+        easy.set_mime_post(mime)?;
+
+        Ok(CrashReportSender::LibCurl { easy })
+    }
+
+    #[cfg(mock)]
+    fn send_with_mock_libcurl(
+        &self,
+        _extra_json_data: String,
+    ) -> std::io::Result<CrashReportSender> {
+        MockLibCurl
+            .get(|f| f(&self))
+            .map(|response| CrashReportSender::MockLibCurl { response })
+    }
+}
+
+pub enum CrashReportSender {
+    CurlChild {
+        child: Child,
+        extra_json_data: String,
+    },
+    LibCurl {
+        easy: super::libcurl::Easy<'static>,
+    },
+    #[cfg(mock)]
+    MockLibCurl {
+        response: std::io::Result<String>,
+    },
+}
+
+impl CrashReportSender {
+    pub fn finish(self) -> anyhow::Result<Response> {
+        let response = match self {
+            Self::CurlChild {
+                mut child,
+                extra_json_data,
+            } => {
+                {
+                    let mut stdin = child
+                        .stdin
+                        .take()
+                        .context("failed to get curl process stdin")?;
+                    std::io::copy(&mut std::io::Cursor::new(extra_json_data), &mut stdin)
+                        .context("failed to write extra file data to stdin of curl process")?;
+                    // stdin is dropped at the end of this scope so that the stream gets an EOF,
+                    // otherwise curl will wait for more input.
+                }
+                let output = child
+                    .wait_with_output()
+                    .context("failed to wait on curl process")?;
+                anyhow::ensure!(
+                    output.status.success(),
+                    "process failed (exit status {}) with stderr: {}",
+                    output.status,
+                    String::from_utf8_lossy(&output.stderr)
+                );
+                String::from_utf8_lossy(&output.stdout).into_owned()
+            }
+            Self::LibCurl { easy } => {
+                let response = easy.perform()?;
+                let response_code = easy.get_response_code()?;
+
+                let response = String::from_utf8_lossy(&response).into_owned();
+                dbg!(&response, &response_code);
+
+                anyhow::ensure!(
+                    response_code == 200,
+                    "unexpected response code ({response_code}): {response}"
+                );
+
+                response
+            }
+            #[cfg(mock)]
+            Self::MockLibCurl { response } => response?.into(),
+        };
+
+        log::debug!("received response from sending report: {:?}", &*response);
+        Ok(Response::parse(response))
+    }
+}
+
+/// A parsed response from submitting a crash report.
+#[derive(Default, Debug)]
+pub struct Response {
+    pub crash_id: Option<String>,
+    pub stop_sending_reports_for: Option<String>,
+    pub view_url: Option<String>,
+    pub discarded: bool,
+}
+
+impl Response {
+    /// Parse a server response.
+    ///
+    /// The response should be newline-separated `<key>=<value>` pairs.
+    fn parse<S: AsRef<str>>(response: S) -> Self {
+        let mut ret = Self::default();
+        // Fields may be omitted, and parsing is best-effort but will not produce any errors (just
+        // a default Response struct).
+        for line in response.as_ref().lines() {
+            if let Some((key, value)) = line.split_once('=') {
+                match key {
+                    "StopSendingReportsFor" => {
+                        ret.stop_sending_reports_for = Some(value.to_owned())
+                    }
+                    "Discarded" => ret.discarded = true,
+                    "CrashID" => ret.crash_id = Some(value.to_owned()),
+                    "ViewURL" => ret.view_url = Some(value.to_owned()),
+                    _ => (),
+                }
+            }
+        }
+        ret
+    }
+}
+
+/// Quote a string per https://curl.se/docs/manpage.html#-F.
+/// That is, add quote characters and escape " and \ with backslashes.
+struct CurlQuote<'a>(&'a str);
+impl std::fmt::Display for CurlQuote<'_> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        use std::fmt::Write;
+
+        f.write_char('"')?;
+        const ESCAPE_CHARS: [char; 2] = ['"', '\\'];
+        for substr in self.0.split_inclusive(ESCAPE_CHARS) {
+            // The last string returned by `split_inclusive` may or may not contain the
+            // search character, unfortunately.
+            if substr.ends_with(ESCAPE_CHARS) {
+                // Safe to use a byte offset rather than a character offset because the
+                // ESCAPE_CHARS are each 1 byte in utf8.
+                let (s, escape) = substr.split_at(substr.len() - 1);
+                f.write_str(s)?;
+                f.write_char('\\')?;
+                f.write_str(escape)?;
+            } else {
+                f.write_str(substr)?;
+            }
+        }
+        f.write_char('"')
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/process.rs b/toolkit/crashreporter/client/app/src/process.rs
new file mode 100644
index 0000000000..126e5b533b
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/process.rs
@@ -0,0 +1,23 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Process utility functions.
+
+use crate::std::{ffi::OsStr, process::Command};
+
+/// Return a command configured to run in the background.
+///
+/// This means that no associated console will be opened, when applicable.
+pub fn background_command<S: AsRef<OsStr>>(program: S) -> Command {
+    #[allow(unused_mut)]
+    let mut cmd = Command::new(program);
+    #[cfg(windows)]
+    {
+        #[cfg_attr(mock, allow(unused))]
+        use std::os::windows::process::CommandExt;
+        use windows_sys::Win32::System::Threading::CREATE_NO_WINDOW;
+        cmd.creation_flags(CREATE_NO_WINDOW);
+    }
+    cmd
+}
diff --git a/toolkit/crashreporter/client/app/src/settings.rs b/toolkit/crashreporter/client/app/src/settings.rs
new file mode 100644
index 0000000000..7ea0e4fe26
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/settings.rs
@@ -0,0 +1,39 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+//! Persistent settings of the application.
+
+#[derive(Debug, serde::Serialize, serde::Deserialize)]
+pub struct Settings {
+    /// Whether a crash report should be sent.
+    pub submit_report: bool,
+    /// Whether the URL that was open should be included in a sent report.
+    pub include_url: bool,
+}
+
+impl Default for Settings {
+    fn default() -> Self {
+        Settings {
+            submit_report: true,
+            include_url: false,
+        }
+    }
+}
+
+impl Settings {
+    /// Write the settings to the given writer.
+    pub fn to_writer<W: std::io::Write>(&self, writer: W) -> anyhow::Result<()> {
+        Ok(serde_json::to_writer_pretty(writer, self)?)
+    }
+
+    /// Read the settings from the given reader.
+    pub fn from_reader<R: std::io::Read>(reader: R) -> anyhow::Result<Self> {
+        Ok(serde_json::from_reader(reader)?)
+    }
+
+    #[cfg(test)]
+    pub fn to_string(&self) -> String {
+        serde_json::to_string_pretty(self).unwrap()
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/std/env.rs b/toolkit/crashreporter/client/app/src/std/env.rs
new file mode 100644
index 0000000000..edc22ded8d
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/std/env.rs
@@ -0,0 +1,45 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use super::mock::{mock_key, MockKey};
+pub use std::env::VarError;
+use std::ffi::{OsStr, OsString};
+
+mock_key! {
+    pub struct MockCurrentExe => std::path::PathBuf
+}
+
+pub struct ArgsOs {
+    argv0: Option<OsString>,
+}
+
+impl Iterator for ArgsOs {
+    type Item = OsString;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        Some(
+            self.argv0
+                .take()
+                .expect("only argv[0] is available when mocked"),
+        )
+    }
+}
+
+pub fn var<K: AsRef<OsStr>>(_key: K) -> Result<String, VarError> {
+    unimplemented!("no var access in tests")
+}
+
+pub fn var_os<K: AsRef<OsStr>>(_key: K) -> Option<OsString> {
+    unimplemented!("no var access in tests")
+}
+
+pub fn args_os() -> ArgsOs {
+    MockCurrentExe.get(|r| ArgsOs {
+        argv0: Some(r.clone().into()),
+    })
+}
+
+pub fn current_exe() -> std::io::Result<super::path::PathBuf> {
+    Ok(MockCurrentExe.get(|r| r.clone().into()))
+}
diff --git a/toolkit/crashreporter/client/app/src/std/fs.rs b/toolkit/crashreporter/client/app/src/std/fs.rs
new file mode 100644
index 0000000000..8ba2c572d5
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/std/fs.rs
@@ -0,0 +1,559 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use crate::std::mock::{mock_key, MockKey};
+use std::collections::HashMap;
+use std::ffi::OsString;
+use std::io::{ErrorKind, Read, Result, Seek, SeekFrom, Write};
+use std::path::{Path, PathBuf};
+use std::sync::{Arc, Mutex};
+use std::time::SystemTime;
+
+/// Mock filesystem file content.
+#[derive(Debug, Default, Clone)]
+pub struct MockFileContent(Arc<Mutex<Vec<u8>>>);
+
+impl MockFileContent {
+    pub fn empty() -> Self {
+        Self::default()
+    }
+
+    pub fn new(data: String) -> Self {
+        Self::new_bytes(data.into())
+    }
+
+    pub fn new_bytes(data: Vec<u8>) -> Self {
+        MockFileContent(Arc::new(Mutex::new(data)))
+    }
+}
+
+impl From<()> for MockFileContent {
+    fn from(_: ()) -> Self {
+        Self::empty()
+    }
+}
+
+impl From<String> for MockFileContent {
+    fn from(s: String) -> Self {
+        Self::new(s)
+    }
+}
+
+impl From<&str> for MockFileContent {
+    fn from(s: &str) -> Self {
+        Self::new(s.to_owned())
+    }
+}
+
+impl From<Vec<u8>> for MockFileContent {
+    fn from(bytes: Vec<u8>) -> Self {
+        Self::new_bytes(bytes)
+    }
+}
+
+impl From<&[u8]> for MockFileContent {
+    fn from(bytes: &[u8]) -> Self {
+        Self::new_bytes(bytes.to_owned())
+    }
+}
+
+/// Mocked filesystem directory entries.
+pub type MockDirEntries = HashMap<OsString, MockFSItem>;
+
+/// The content of a mock filesystem item.
+pub enum MockFSContent {
+    /// File content.
+    File(Result<MockFileContent>),
+    /// A directory with the given entries.
+    Dir(MockDirEntries),
+}
+
+impl std::fmt::Debug for MockFSContent {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        match self {
+            Self::File(_) => f.debug_tuple("File").finish(),
+            Self::Dir(e) => f.debug_tuple("Dir").field(e).finish(),
+        }
+    }
+}
+
+/// A mock filesystem item.
+#[derive(Debug)]
+pub struct MockFSItem {
+    /// The content of the item (file/dir).
+    pub content: MockFSContent,
+    /// The modification time of the item.
+    pub modified: SystemTime,
+}
+
+impl From<MockFSContent> for MockFSItem {
+    fn from(content: MockFSContent) -> Self {
+        MockFSItem {
+            content,
+            modified: SystemTime::UNIX_EPOCH,
+        }
+    }
+}
+
+/// A mock filesystem.
+#[derive(Debug, Clone)]
+pub struct MockFiles {
+    root: Arc<Mutex<MockFSItem>>,
+}
+
+impl Default for MockFiles {
+    fn default() -> Self {
+        MockFiles {
+            root: Arc::new(Mutex::new(MockFSContent::Dir(Default::default()).into())),
+        }
+    }
+}
+
+impl MockFiles {
+    /// Create a new, empty filesystem.
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Add a mocked file with the given content. The modification time will be the unix epoch.
+    ///
+    /// Pancis if the parent directory is not already mocked.
+    pub fn add_file<P: AsRef<Path>, C: Into<MockFileContent>>(&self, path: P, content: C) -> &Self {
+        self.add_file_result(path, Ok(content.into()), SystemTime::UNIX_EPOCH)
+    }
+
+    /// Add a mocked directory.
+    pub fn add_dir<P: AsRef<Path>>(&self, path: P) -> &Self {
+        self.path(path, true, |_| ()).unwrap();
+        self
+    }
+
+    /// Add a mocked file that returns the given result and has the given modification time.
+    ///
+    /// Pancis if the parent directory is not already mocked.
+    pub fn add_file_result<P: AsRef<Path>>(
+        &self,
+        path: P,
+        result: Result<MockFileContent>,
+        modified: SystemTime,
+    ) -> &Self {
+        let name = path.as_ref().file_name().expect("invalid path");
+        self.parent_dir(path.as_ref(), move |dir| {
+            if dir.contains_key(name) {
+                Err(ErrorKind::AlreadyExists.into())
+            } else {
+                dir.insert(
+                    name.to_owned(),
+                    MockFSItem {
+                        content: MockFSContent::File(result),
+                        modified,
+                    },
+                );
+                Ok(())
+            }
+        })
+        .and_then(|r| r)
+        .unwrap();
+        self
+    }
+
+    /// If create_dirs is true, all missing path components (_including the final component_) are
+    /// created as directories. In this case `Err` is only returned if a file conflicts with
+    /// a directory component.
+    pub fn path<P: AsRef<Path>, F, R>(&self, path: P, create_dirs: bool, f: F) -> Result<R>
+    where
+        F: FnOnce(&mut MockFSItem) -> R,
+    {
+        let mut guard = self.root.lock().unwrap();
+        let mut cur_entry = &mut *guard;
+        for component in path.as_ref().components() {
+            use std::path::Component::*;
+            match component {
+                CurDir | RootDir | Prefix(_) => continue,
+                ParentDir => panic!("unsupported path: {}", path.as_ref().display()),
+                Normal(name) => {
+                    let cur_dir = match &mut cur_entry.content {
+                        MockFSContent::File(_) => return Err(ErrorKind::NotFound.into()),
+                        MockFSContent::Dir(d) => d,
+                    };
+                    cur_entry = if create_dirs {
+                        cur_dir
+                            .entry(name.to_owned())
+                            .or_insert_with(|| MockFSContent::Dir(Default::default()).into())
+                    } else {
+                        cur_dir.get_mut(name).ok_or(ErrorKind::NotFound)?
+                    };
+                }
+            }
+        }
+        Ok(f(cur_entry))
+    }
+
+    /// Get the mocked parent directory of the given path and call a callback on the mocked
+    /// directory's entries.
+    pub fn parent_dir<P: AsRef<Path>, F, R>(&self, path: P, f: F) -> Result<R>
+    where
+        F: FnOnce(&mut MockDirEntries) -> R,
+    {
+        self.path(
+            path.as_ref().parent().unwrap_or(&Path::new("")),
+            false,
+            move |item| match &mut item.content {
+                MockFSContent::File(_) => Err(ErrorKind::NotFound.into()),
+                MockFSContent::Dir(d) => Ok(f(d)),
+            },
+        )
+        .and_then(|r| r)
+    }
+
+    /// Return a file assertion helper for the mocked filesystem.
+    pub fn assert_files(&self) -> AssertFiles {
+        let mut files = HashMap::new();
+        let root = self.root.lock().unwrap();
+
+        fn dir(files: &mut HashMap<PathBuf, MockFileContent>, path: &Path, item: &MockFSItem) {
+            match &item.content {
+                MockFSContent::File(Ok(c)) => {
+                    files.insert(path.to_owned(), c.clone());
+                }
+                MockFSContent::Dir(d) => {
+                    for (component, item) in d {
+                        dir(files, &path.join(component), item);
+                    }
+                }
+                _ => (),
+            }
+        }
+        dir(&mut files, Path::new(""), &*root);
+        AssertFiles { files }
+    }
+}
+
+/// A utility for asserting the state of the mocked filesystem.
+///
+/// All files must be accounted for; when dropped, a panic will occur if some files remain which
+/// weren't checked.
+#[derive(Debug)]
+pub struct AssertFiles {
+    files: HashMap<PathBuf, MockFileContent>,
+}
+
+// On windows we ignore drive prefixes. This is only relevant for real paths, which are only
+// present for edge case situations in tests (where AssertFiles is used).
+fn remove_prefix(p: &Path) -> &Path {
+    let mut iter = p.components();
+    if let Some(std::path::Component::Prefix(_)) = iter.next() {
+        iter.next(); // Prefix is followed by RootDir
+        iter.as_path()
+    } else {
+        p
+    }
+}
+
+impl AssertFiles {
+    /// Assert that the given path contains the given content (as a utf8 string).
+    pub fn check<P: AsRef<Path>, S: AsRef<str>>(&mut self, path: P, content: S) -> &mut Self {
+        let p = remove_prefix(path.as_ref());
+        let Some(mfc) = self.files.remove(p) else {
+            panic!("missing file: {}", p.display());
+        };
+        let guard = mfc.0.lock().unwrap();
+        assert_eq!(
+            std::str::from_utf8(&*guard).unwrap(),
+            content.as_ref(),
+            "file content mismatch: {}",
+            p.display()
+        );
+        self
+    }
+
+    /// Assert that the given path contains the given byte content.
+    pub fn check_bytes<P: AsRef<Path>, B: AsRef<[u8]>>(
+        &mut self,
+        path: P,
+        content: B,
+    ) -> &mut Self {
+        let p = remove_prefix(path.as_ref());
+        let Some(mfc) = self.files.remove(p) else {
+            panic!("missing file: {}", p.display());
+        };
+        let guard = mfc.0.lock().unwrap();
+        assert_eq!(
+            &*guard,
+            content.as_ref(),
+            "file content mismatch: {}",
+            p.display()
+        );
+        self
+    }
+
+    /// Ignore the given file (whether it exists or not).
+    pub fn ignore<P: AsRef<Path>>(&mut self, path: P) -> &mut Self {
+        self.files.remove(remove_prefix(path.as_ref()));
+        self
+    }
+
+    /// Assert that the given path exists without checking its content.
+    pub fn check_exists<P: AsRef<Path>>(&mut self, path: P) -> &mut Self {
+        let p = remove_prefix(path.as_ref());
+        if self.files.remove(p).is_none() {
+            panic!("missing file: {}", p.display());
+        }
+        self
+    }
+
+    /// Finish checking files.
+    ///
+    /// This panics if all files were not checked.
+    ///
+    /// This is also called when the value is dropped.
+    pub fn finish(&mut self) {
+        let files = std::mem::take(&mut self.files);
+        if !files.is_empty() {
+            panic!("additional files not expected: {:?}", files.keys());
+        }
+    }
+}
+
+impl Drop for AssertFiles {
+    fn drop(&mut self) {
+        if !std::thread::panicking() {
+            self.finish();
+        }
+    }
+}
+
+mock_key! {
+    pub struct MockFS => MockFiles
+}
+
+pub struct File {
+    content: MockFileContent,
+    pos: usize,
+}
+
+impl File {
+    pub fn open<P: AsRef<Path>>(path: P) -> Result<File> {
+        MockFS.get(move |files| {
+            files
+                .path(path, false, |item| match &item.content {
+                    MockFSContent::File(result) => result
+                        .as_ref()
+                        .map(|b| File {
+                            content: b.clone(),
+                            pos: 0,
+                        })
+                        .map_err(|e| e.kind().into()),
+                    MockFSContent::Dir(_) => Err(ErrorKind::NotFound.into()),
+                })
+                .and_then(|r| r)
+        })
+    }
+
+    pub fn create<P: AsRef<Path>>(path: P) -> Result<File> {
+        let path = path.as_ref();
+        MockFS.get(|files| {
+            let name = path.file_name().expect("invalid path");
+            files.parent_dir(path, move |d| {
+                if !d.contains_key(name) {
+                    d.insert(
+                        name.to_owned(),
+                        MockFSItem {
+                            content: MockFSContent::File(Ok(Default::default())),
+                            modified: super::time::SystemTime::now().0,
+                        },
+                    );
+                }
+            })
+        })?;
+        Self::open(path)
+    }
+}
+
+impl Read for File {
+    fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
+        let guard = self.content.0.lock().unwrap();
+        if self.pos >= guard.len() {
+            return Ok(0);
+        }
+        let to_read = std::cmp::min(buf.len(), guard.len() - self.pos);
+        buf[..to_read].copy_from_slice(&guard[self.pos..self.pos + to_read]);
+        self.pos += to_read;
+        Ok(to_read)
+    }
+}
+
+impl Seek for File {
+    fn seek(&mut self, pos: SeekFrom) -> Result<u64> {
+        let len = self.content.0.lock().unwrap().len();
+        match pos {
+            SeekFrom::Start(n) => self.pos = n as usize,
+            SeekFrom::End(n) => {
+                if n < 0 {
+                    let offset = -n as usize;
+                    if offset > len {
+                        return Err(std::io::Error::new(
+                            std::io::ErrorKind::InvalidInput,
+                            "out of bounds",
+                        ));
+                    }
+                    self.pos = len - offset;
+                } else {
+                    self.pos = len + n as usize
+                }
+            }
+            SeekFrom::Current(n) => {
+                if n < 0 {
+                    let offset = -n as usize;
+                    if offset > self.pos {
+                        return Err(std::io::Error::new(
+                            std::io::ErrorKind::InvalidInput,
+                            "out of bounds",
+                        ));
+                    }
+                    self.pos -= offset;
+                } else {
+                    self.pos += n as usize;
+                }
+            }
+        }
+        Ok(self.pos as u64)
+    }
+}
+
+impl Write for File {
+    fn write(&mut self, buf: &[u8]) -> Result<usize> {
+        let mut guard = self.content.0.lock().unwrap();
+        let end = self.pos + buf.len();
+        if end > guard.len() {
+            guard.resize(end, 0);
+        }
+        (&mut guard[self.pos..end]).copy_from_slice(buf);
+        self.pos = end;
+        Ok(buf.len())
+    }
+
+    fn flush(&mut self) -> Result<()> {
+        Ok(())
+    }
+}
+
+pub fn create_dir_all<P: AsRef<Path>>(path: P) -> Result<()> {
+    MockFS.get(move |files| files.path(path, true, |_| ()))
+}
+
+pub fn rename<P: AsRef<Path>, Q: AsRef<Path>>(from: P, to: Q) -> Result<()> {
+    MockFS.get(move |files| {
+        let from_name = from.as_ref().file_name().expect("invalid path");
+        let item = files
+            .parent_dir(from.as_ref(), move |d| {
+                d.remove(from_name).ok_or(ErrorKind::NotFound.into())
+            })
+            .and_then(|r| r)?;
+
+        let to_name = to.as_ref().file_name().expect("invalid path");
+        files
+            .parent_dir(to.as_ref(), move |d| {
+                // Just error if `to` exists, which doesn't quite follow `std::fs::rename` behavior.
+                if d.contains_key(to_name) {
+                    Err(ErrorKind::AlreadyExists.into())
+                } else {
+                    d.insert(to_name.to_owned(), item);
+                    Ok(())
+                }
+            })
+            .and_then(|r| r)
+    })
+}
+
+pub fn remove_file<P: AsRef<Path>>(path: P) -> Result<()> {
+    MockFS.get(move |files| {
+        let name = path.as_ref().file_name().expect("invalid path");
+        files
+            .parent_dir(path.as_ref(), |d| {
+                if let Some(MockFSItem {
+                    content: MockFSContent::Dir(_),
+                    ..
+                }) = d.get(name)
+                {
+                    Err(ErrorKind::NotFound.into())
+                } else {
+                    d.remove(name).ok_or(ErrorKind::NotFound.into()).map(|_| ())
+                }
+            })
+            .and_then(|r| r)
+    })
+}
+
+pub fn write<P: AsRef<Path>, C: AsRef<[u8]>>(path: P, contents: C) -> Result<()> {
+    File::create(path.as_ref())?.write_all(contents.as_ref())
+}
+
+pub struct ReadDir {
+    base: PathBuf,
+    children: Vec<OsString>,
+}
+
+impl ReadDir {
+    pub fn new(path: &Path) -> Result<Self> {
+        MockFS.get(move |files| {
+            files
+                .path(path, false, |item| match &item.content {
+                    MockFSContent::Dir(d) => Ok(ReadDir {
+                        base: path.to_owned(),
+                        children: d.keys().cloned().collect(),
+                    }),
+                    MockFSContent::File(_) => Err(ErrorKind::NotFound.into()),
+                })
+                .and_then(|r| r)
+        })
+    }
+}
+
+impl Iterator for ReadDir {
+    type Item = Result<DirEntry>;
+    fn next(&mut self) -> Option<Self::Item> {
+        let child = self.children.pop()?;
+        Some(Ok(DirEntry(self.base.join(child))))
+    }
+}
+
+pub struct DirEntry(PathBuf);
+
+impl DirEntry {
+    pub fn path(&self) -> super::path::PathBuf {
+        super::path::PathBuf(self.0.clone())
+    }
+
+    pub fn metadata(&self) -> Result<Metadata> {
+        MockFS.get(|files| {
+            files.path(&self.0, false, |item| {
+                let is_dir = matches!(&item.content, MockFSContent::Dir(_));
+                Metadata {
+                    is_dir,
+                    modified: item.modified,
+                }
+            })
+        })
+    }
+}
+
+pub struct Metadata {
+    is_dir: bool,
+    modified: SystemTime,
+}
+
+impl Metadata {
+    pub fn is_file(&self) -> bool {
+        !self.is_dir
+    }
+
+    pub fn is_dir(&self) -> bool {
+        self.is_dir
+    }
+
+    pub fn modified(&self) -> Result<super::time::SystemTime> {
+        Ok(super::time::SystemTime(self.modified))
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/std/mock.rs b/toolkit/crashreporter/client/app/src/std/mock.rs
new file mode 100644
index 0000000000..ed942a09bd
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/std/mock.rs
@@ -0,0 +1,254 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Mocking utilities.
+//!
+//! Mock data is set on a per-thread basis. [`crate::std::thread`] handles this automatically for
+//! scoped threads, and warns about creating threads otherwise (which won't be able to
+//! automatically share mocked data, but it can be easily done with [`SharedMockData`] when
+//! appropriate).
+//!
+//! Mock data is stored using type erasure, with a [`MockKey`] indexing arbitrary values. Use
+//! [`mock_key!`] to define keys and the values to which they map. This approach was taken as a
+//! matter of covenience for programmers, and the resulting creation and consumption APIs are
+//! succinct yet extensible.
+//!
+//! Consumers should define keys (and expose them for mockers), and at runtime create a mock key
+//! instance and call [`MockKey::get`] or [`MockKey::try_get`] to retrieve mocked values to use.
+//!
+//! Mockers should call [`builder`] to create a builder, [`set`](Builder::set) key/value mappings,
+//! and call [`run`](Builder::run) to execute code with the mock data set.
+
+use std::any::{Any, TypeId};
+use std::collections::{hash_map::DefaultHasher, HashMap};
+use std::hash::{Hash, Hasher};
+use std::sync::atomic::{AtomicPtr, Ordering::Relaxed};
+
+type MockDataMap = HashMap<Box<dyn MockKeyStored>, Box<dyn Any + Send + Sync>>;
+
+thread_local! {
+    static MOCK_DATA: AtomicPtr<MockDataMap> = Default::default();
+}
+
+/// A trait intended to be used as a trait object interface for mock keys.
+pub trait MockKeyStored: Any + std::fmt::Debug + Sync {
+    fn eq(&self, other: &dyn MockKeyStored) -> bool;
+    fn hash(&self, state: &mut DefaultHasher);
+}
+
+impl PartialEq for dyn MockKeyStored {
+    fn eq(&self, other: &Self) -> bool {
+        MockKeyStored::eq(self, other)
+    }
+}
+
+impl Eq for dyn MockKeyStored {}
+
+impl Hash for dyn MockKeyStored {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.type_id().hash(state);
+        let mut hasher = DefaultHasher::new();
+        MockKeyStored::hash(self, &mut hasher);
+        state.write_u64(hasher.finish());
+    }
+}
+
+impl dyn MockKeyStored {
+    pub fn downcast_ref<T: Any>(&self) -> Option<&T> {
+        if self.type_id() == TypeId::of::<T>() {
+            Some(unsafe { &*(self as *const _ as *const T) })
+        } else {
+            None
+        }
+    }
+}
+
+/// A type which can be used as a mock key.
+pub trait MockKey: MockKeyStored + Sized {
+    /// The value to which the key maps.
+    type Value: Any + Send + Sync;
+
+    /// Get the value set for this key, returning `None` if no data is set.
+    fn try_get<F, R>(&self, f: F) -> Option<R>
+    where
+        F: FnOnce(&Self::Value) -> R,
+    {
+        MOCK_DATA.with(move |ptr| {
+            let ptr = ptr.load(Relaxed);
+            if ptr.is_null() {
+                panic!("no mock data set");
+            }
+            unsafe { &*ptr }
+                .get(self as &dyn MockKeyStored)
+                .and_then(move |b| b.downcast_ref())
+                .map(f)
+        })
+    }
+
+    /// Get the value set for this key.
+    ///
+    /// Panics if no mock data is set for the key.
+    fn get<F, R>(&self, f: F) -> R
+    where
+        F: FnOnce(&Self::Value) -> R,
+    {
+        match self.try_get(f) {
+            Some(v) => v,
+            None => panic!("mock data for {self:?} not set"),
+        }
+    }
+}
+
+/// Mock data which can be shared amongst threads.
+pub struct SharedMockData(AtomicPtr<MockDataMap>);
+
+impl Clone for SharedMockData {
+    fn clone(&self) -> Self {
+        SharedMockData(AtomicPtr::new(self.0.load(Relaxed)))
+    }
+}
+
+impl SharedMockData {
+    /// Create a `SharedMockData` which stores the mock data from the current thread.
+    pub fn new() -> Self {
+        MOCK_DATA.with(|ptr| SharedMockData(AtomicPtr::new(ptr.load(Relaxed))))
+    }
+
+    /// Set the mock data on the current thread.
+    ///
+    /// # Safety
+    /// Callers must ensure that the mock data outlives the lifetime of the thread.
+    pub unsafe fn set(self) {
+        MOCK_DATA.with(|ptr| ptr.store(self.0.into_inner(), Relaxed));
+    }
+}
+
+/// Create a mock builder, which allows adding mock data and running functions under that mock
+/// environment.
+pub fn builder() -> Builder {
+    Builder::new()
+}
+
+/// A mock data builder.
+#[derive(Default)]
+pub struct Builder {
+    data: MockDataMap,
+}
+
+impl Builder {
+    /// Create a new, empty builder.
+    pub fn new() -> Self {
+        Default::default()
+    }
+
+    /// Set a mock data key/value mapping.
+    pub fn set<K: MockKey>(&mut self, key: K, value: K::Value) -> &mut Self {
+        self.data.insert(Box::new(key), Box::new(value));
+        self
+    }
+
+    /// Run the given function with mock data set.
+    pub fn run<F, R>(&mut self, f: F) -> R
+    where
+        F: FnOnce() -> R,
+    {
+        MOCK_DATA.with(|ptr| ptr.store(&mut self.data, Relaxed));
+        let ret = f();
+        MOCK_DATA.with(|ptr| ptr.store(std::ptr::null_mut(), Relaxed));
+        ret
+    }
+}
+
+/// A general-purpose [`MockKey`] keyed by an identifier string and the stored type.
+///
+/// Use [`hook`] or [`try_hook`] in code accessing the values.
+pub struct MockHook<T> {
+    name: &'static str,
+    _p: std::marker::PhantomData<fn() -> T>,
+}
+
+impl<T> std::fmt::Debug for MockHook<T> {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        f.debug_struct(&format!("MockHook<{}>", std::any::type_name::<T>()))
+            .field("name", &self.name)
+            .finish()
+    }
+}
+
+impl<T: 'static> MockKeyStored for MockHook<T> {
+    fn eq(&self, other: &dyn MockKeyStored) -> bool {
+        std::any::TypeId::of::<Self>() == other.type_id()
+            && self.name == other.downcast_ref::<Self>().unwrap().name
+    }
+    fn hash(&self, state: &mut DefaultHasher) {
+        self.name.hash(state)
+    }
+}
+
+impl<T: Any + Send + Sync + 'static> MockKey for MockHook<T> {
+    type Value = T;
+}
+
+impl<T> MockHook<T> {
+    /// Create a new mock hook key with the given name.
+    pub fn new(name: &'static str) -> Self {
+        MockHook {
+            name,
+            _p: Default::default(),
+        }
+    }
+}
+
+/// Create a mock hook with the given name. When mocking isn't enabled, the given value will be
+/// used instead. Panics if the hook isn't set.
+pub fn hook<T: Any + Send + Sync + Clone>(_normally: T, name: &'static str) -> T {
+    MockHook::new(name).get(|v: &T| v.clone())
+}
+
+/// Create a mock hook with the given name. When mocking isn't enabled or the hook hasn't been set,
+/// the given value will be used instead.
+pub fn try_hook<T: Any + Send + Sync + Clone>(fallback: T, name: &'static str) -> T {
+    MockHook::new(name)
+        .try_get(|v: &T| v.clone())
+        .unwrap_or(fallback)
+}
+
+/// Create a mock key with an associated value type.
+///
+/// Supports the following syntaxes:
+/// * Unit struct: `<visibility> struct NAME => VALUE_TYPE`
+/// * Tuple struct: `<visibility> struct NAME(ITEMS) => VALUE_TYPE`
+/// * Normal struct: `<visibility> struct NAME { FIELDS } => VALUE_TYPE`
+macro_rules! mock_key {
+    ( $vis:vis struct $name:ident => $value:ty ) => {
+        $crate::std::mock::mock_key! { @structdef[$vis struct $name;] $name $value }
+    };
+    ( $vis:vis struct $name:ident ($($tuple:tt)*) => $value:ty ) => {
+        $crate::std::mock::mock_key! { @structdef[$vis struct $name($($tuple)*);] $name $value }
+    };
+    ( $vis:vis struct $name:ident {$($full:tt)*} => $value:ty ) => {
+        $crate::std::mock::mock_key! { @structdef[$vis struct $name{$($full)*}] $name $value }
+    };
+    ( @structdef [$($def:tt)+] $name:ident $value:ty ) => {
+        #[derive(Debug, PartialEq, Eq, Hash)]
+        $($def)+
+
+        impl crate::std::mock::MockKeyStored for $name {
+            fn eq(&self, other: &dyn crate::std::mock::MockKeyStored) -> bool {
+                std::any::TypeId::of::<Self>() == other.type_id()
+                    && PartialEq::eq(self, other.downcast_ref::<Self>().unwrap())
+            }
+
+            fn hash(&self, state: &mut std::collections::hash_map::DefaultHasher) {
+                std::hash::Hash::hash(self, state)
+            }
+        }
+
+        impl crate::std::mock::MockKey for $name {
+            type Value = $value;
+        }
+    }
+}
+
+pub(crate) use mock_key;
diff --git a/toolkit/crashreporter/client/app/src/std/mock_stub.rs b/toolkit/crashreporter/client/app/src/std/mock_stub.rs
new file mode 100644
index 0000000000..a02ac3dea1
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/std/mock_stub.rs
@@ -0,0 +1,20 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+#![allow(dead_code)]
+
+//! Stubs used when mocking isn't enabled.
+
+/// Create a mock hook with the given name. When mocking isn't enabled, the given value will be
+/// used instead. Panics if the hook isn't set.
+#[inline(always)]
+pub fn hook<T: std::any::Any + Send + Sync + Clone>(normally: T, _name: &'static str) -> T {
+    normally
+}
+
+/// Create a mock hook with the given name. When mocking isn't enabled or the hook hasn't been set,
+/// the given value will be used instead.
+#[inline(always)]
+pub fn try_hook<T: std::any::Any + Send + Sync + Clone>(fallback: T, _name: &'static str) -> T {
+    fallback
+}
diff --git a/toolkit/crashreporter/client/app/src/std/mod.rs b/toolkit/crashreporter/client/app/src/std/mod.rs
new file mode 100644
index 0000000000..467d6b0c14
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/std/mod.rs
@@ -0,0 +1,33 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Standard library wrapper (for mocking in tests).
+//!
+//! In general this should always be used rather than `std` directly, and _especially_ when using
+//! `std` functions and types which interact with the runtime host environment.
+//!
+//! Note that, in some cases, this wrapper extends the `std` library. Notably, the [`mock`] module
+//! adds mocking functions.
+
+#![cfg_attr(mock, allow(unused))]
+
+pub use std::*;
+
+#[cfg_attr(not(mock), path = "mock_stub.rs")]
+pub mod mock;
+
+#[cfg(mock)]
+pub mod env;
+#[cfg(mock)]
+pub mod fs;
+#[cfg(mock)]
+pub mod net;
+#[cfg(mock)]
+pub mod path;
+#[cfg(mock)]
+pub mod process;
+#[cfg(mock)]
+pub mod thread;
+#[cfg(mock)]
+pub mod time;
diff --git a/toolkit/crashreporter/client/app/src/std/net.rs b/toolkit/crashreporter/client/app/src/std/net.rs
new file mode 100644
index 0000000000..dd51a44756
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/std/net.rs
@@ -0,0 +1,5 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Stub to avoid net use, if any.
diff --git a/toolkit/crashreporter/client/app/src/std/path.rs b/toolkit/crashreporter/client/app/src/std/path.rs
new file mode 100644
index 0000000000..c565615514
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/std/path.rs
@@ -0,0 +1,157 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! We unfortunately have to mock `Path` because of `exists`, `try_exists`, and `metadata`.
+
+pub use std::path::*;
+
+use super::mock::MockKey;
+use std::ffi::OsStr;
+
+macro_rules! delegate {
+    ( fn $name:ident (&self $(, $arg:ident : $argty:ty )* ) -> $ret:ty ) => {
+        pub fn $name (&self, $($arg : $ty)*) -> $ret {
+            self.0.$name($($arg),*)
+        }
+    }
+}
+
+#[repr(transparent)]
+#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct Path(std::path::Path);
+
+impl AsRef<std::path::Path> for Path {
+    fn as_ref(&self) -> &std::path::Path {
+        &self.0
+    }
+}
+
+impl AsRef<OsStr> for Path {
+    fn as_ref(&self) -> &OsStr {
+        self.0.as_ref()
+    }
+}
+
+impl AsRef<Path> for &str {
+    fn as_ref(&self) -> &Path {
+        Path::from_path(self.as_ref())
+    }
+}
+
+impl AsRef<Path> for String {
+    fn as_ref(&self) -> &Path {
+        Path::from_path(self.as_ref())
+    }
+}
+
+impl AsRef<Path> for &OsStr {
+    fn as_ref(&self) -> &Path {
+        Path::from_path(self.as_ref())
+    }
+}
+
+impl Path {
+    fn from_path(path: &std::path::Path) -> &Self {
+        // # Safety
+        // Transparent wrapper is safe to transmute.
+        unsafe { std::mem::transmute(path) }
+    }
+
+    pub fn exists(&self) -> bool {
+        super::fs::MockFS
+            .try_get(|files| {
+                files
+                    .path(self, false, |item| match &item.content {
+                        super::fs::MockFSContent::File(r) => r.is_ok(),
+                        _ => true,
+                    })
+                    .unwrap_or(false)
+            })
+            .unwrap_or(false)
+    }
+
+    pub fn read_dir(&self) -> super::io::Result<super::fs::ReadDir> {
+        super::fs::ReadDir::new(&self.0)
+    }
+
+    delegate!(fn display(&self) -> Display);
+    delegate!(fn file_stem(&self) -> Option<&OsStr>);
+    delegate!(fn file_name(&self) -> Option<&OsStr>);
+    delegate!(fn extension(&self) -> Option<&OsStr>);
+
+    pub fn join<P: AsRef<Path>>(&self, path: P) -> PathBuf {
+        PathBuf(self.0.join(&path.as_ref().0))
+    }
+
+    pub fn parent(&self) -> Option<&Path> {
+        self.0.parent().map(Path::from_path)
+    }
+}
+
+#[repr(transparent)]
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct PathBuf(pub(super) std::path::PathBuf);
+
+impl PathBuf {
+    pub fn set_extension<S: AsRef<OsStr>>(&mut self, extension: S) -> bool {
+        self.0.set_extension(extension)
+    }
+
+    pub fn push<P: AsRef<Path>>(&mut self, path: P) {
+        self.0.push(path.as_ref())
+    }
+
+    pub fn pop(&mut self) -> bool {
+        self.0.pop()
+    }
+}
+
+impl std::ops::Deref for PathBuf {
+    type Target = Path;
+    fn deref(&self) -> &Self::Target {
+        Path::from_path(self.0.as_ref())
+    }
+}
+
+impl AsRef<Path> for PathBuf {
+    fn as_ref(&self) -> &Path {
+        Path::from_path(self.0.as_ref())
+    }
+}
+
+impl AsRef<std::path::Path> for PathBuf {
+    fn as_ref(&self) -> &std::path::Path {
+        self.0.as_ref()
+    }
+}
+
+impl AsRef<OsStr> for PathBuf {
+    fn as_ref(&self) -> &OsStr {
+        self.0.as_ref()
+    }
+}
+
+impl From<std::ffi::OsString> for PathBuf {
+    fn from(os_str: std::ffi::OsString) -> Self {
+        PathBuf(os_str.into())
+    }
+}
+
+impl From<std::path::PathBuf> for PathBuf {
+    fn from(pathbuf: std::path::PathBuf) -> Self {
+        PathBuf(pathbuf)
+    }
+}
+
+impl From<PathBuf> for std::ffi::OsString {
+    fn from(pathbuf: PathBuf) -> Self {
+        pathbuf.0.into()
+    }
+}
+
+impl From<&str> for PathBuf {
+    fn from(s: &str) -> Self {
+        PathBuf(s.into())
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/std/process.rs b/toolkit/crashreporter/client/app/src/std/process.rs
new file mode 100644
index 0000000000..49dd028447
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/std/process.rs
@@ -0,0 +1,201 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+pub use std::process::*;
+
+use crate::std::mock::{mock_key, MockKey};
+
+use std::ffi::{OsStr, OsString};
+use std::io::Result;
+use std::sync::{Arc, Mutex};
+
+mock_key! {
+    // Uses PathBuf rather than OsString to avoid path separator differences.
+    pub struct MockCommand(::std::path::PathBuf) => Box<dyn Fn(&Command) -> Result<Output> + Send + Sync>
+}
+
+#[derive(Debug)]
+pub struct Command {
+    pub program: OsString,
+    pub args: Vec<OsString>,
+    pub env: std::collections::HashMap<OsString, OsString>,
+    pub stdin: Vec<u8>,
+    // XXX The spawn stuff is hacky, but for now there's only one case where we really need to
+    // interact with `spawn` so we live with it for testing.
+    pub spawning: bool,
+    pub spawned_child: Mutex<Option<::std::process::Child>>,
+}
+
+impl Command {
+    pub fn mock<S: AsRef<OsStr>>(program: S) -> MockCommand {
+        MockCommand(program.as_ref().into())
+    }
+
+    pub fn new<S: AsRef<OsStr>>(program: S) -> Self {
+        Command {
+            program: program.as_ref().into(),
+            args: vec![],
+            env: Default::default(),
+            stdin: Default::default(),
+            spawning: false,
+            spawned_child: Mutex::new(None),
+        }
+    }
+
+    pub fn arg<S: AsRef<OsStr>>(&mut self, arg: S) -> &mut Self {
+        self.args.push(arg.as_ref().into());
+        self
+    }
+
+    pub fn args<I, S>(&mut self, args: I) -> &mut Self
+    where
+        I: IntoIterator<Item = S>,
+        S: AsRef<OsStr>,
+    {
+        for arg in args.into_iter() {
+            self.arg(arg);
+        }
+        self
+    }
+
+    pub fn env<K, V>(&mut self, key: K, val: V) -> &mut Self
+    where
+        K: AsRef<OsStr>,
+        V: AsRef<OsStr>,
+    {
+        self.env.insert(key.as_ref().into(), val.as_ref().into());
+        self
+    }
+
+    pub fn stdin<T: Into<Stdio>>(&mut self, _cfg: T) -> &mut Self {
+        self
+    }
+
+    pub fn stdout<T: Into<Stdio>>(&mut self, _cfg: T) -> &mut Self {
+        self
+    }
+
+    pub fn stderr<T: Into<Stdio>>(&mut self, _cfg: T) -> &mut Self {
+        self
+    }
+
+    pub fn output(&mut self) -> std::io::Result<Output> {
+        MockCommand(self.program.as_os_str().into()).get(|f| f(self))
+    }
+
+    pub fn spawn(&mut self) -> std::io::Result<Child> {
+        self.spawning = true;
+        self.output()?;
+        self.spawning = false;
+        let stdin = Arc::new(Mutex::new(vec![]));
+        Ok(Child {
+            stdin: Some(ChildStdin {
+                data: stdin.clone(),
+            }),
+            cmd: self.clone_for_child(),
+            stdin_data: Some(stdin),
+        })
+    }
+
+    #[cfg(windows)]
+    pub fn creation_flags(&mut self, _flags: u32) -> &mut Self {
+        self
+    }
+
+    pub fn output_from_real_command(&self) -> std::io::Result<Output> {
+        let mut spawned_child = self.spawned_child.lock().unwrap();
+        if spawned_child.is_none() {
+            *spawned_child = Some(
+                ::std::process::Command::new(self.program.clone())
+                    .args(self.args.clone())
+                    .envs(self.env.clone())
+                    .stdin(Stdio::piped())
+                    .stdout(Stdio::piped())
+                    .stderr(Stdio::piped())
+                    .spawn()?,
+            );
+        }
+
+        if self.spawning {
+            return Ok(success_output());
+        }
+
+        let mut child = spawned_child.take().unwrap();
+        {
+            let mut input = child.stdin.take().unwrap();
+            std::io::copy(&mut std::io::Cursor::new(&self.stdin), &mut input)?;
+        }
+        child.wait_with_output()
+    }
+
+    fn clone_for_child(&self) -> Self {
+        Command {
+            program: self.program.clone(),
+            args: self.args.clone(),
+            env: self.env.clone(),
+            stdin: self.stdin.clone(),
+            spawning: false,
+            spawned_child: Mutex::new(self.spawned_child.lock().unwrap().take()),
+        }
+    }
+}
+
+pub struct Child {
+    pub stdin: Option<ChildStdin>,
+    cmd: Command,
+    stdin_data: Option<Arc<Mutex<Vec<u8>>>>,
+}
+
+impl Child {
+    pub fn wait_with_output(mut self) -> std::io::Result<Output> {
+        self.ref_wait_with_output().unwrap()
+    }
+
+    fn ref_wait_with_output(&mut self) -> Option<std::io::Result<Output>> {
+        drop(self.stdin.take());
+        if let Some(stdin) = self.stdin_data.take() {
+            self.cmd.stdin = Arc::try_unwrap(stdin)
+                .expect("stdin not dropped, wait_with_output may block")
+                .into_inner()
+                .unwrap();
+            Some(MockCommand(self.cmd.program.as_os_str().into()).get(|f| f(&self.cmd)))
+        } else {
+            None
+        }
+    }
+}
+
+pub struct ChildStdin {
+    data: Arc<Mutex<Vec<u8>>>,
+}
+
+impl std::io::Write for ChildStdin {
+    fn write(&mut self, buf: &[u8]) -> Result<usize> {
+        self.data.lock().unwrap().write(buf)
+    }
+
+    fn flush(&mut self) -> Result<()> {
+        Ok(())
+    }
+}
+
+#[cfg(unix)]
+pub fn success_exit_status() -> ExitStatus {
+    use std::os::unix::process::ExitStatusExt;
+    ExitStatus::from_raw(0)
+}
+
+#[cfg(windows)]
+pub fn success_exit_status() -> ExitStatus {
+    use std::os::windows::process::ExitStatusExt;
+    ExitStatus::from_raw(0)
+}
+
+pub fn success_output() -> Output {
+    Output {
+        status: success_exit_status(),
+        stdout: vec![],
+        stderr: vec![],
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/std/thread.rs b/toolkit/crashreporter/client/app/src/std/thread.rs
new file mode 100644
index 0000000000..d2dc74702a
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/std/thread.rs
@@ -0,0 +1,45 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+pub use std::thread::*;
+
+// Mock `spawn` just to issue a warning that mocking within the thread won't work without manual
+// intervention.
+pub fn spawn<F, T>(f: F) -> JoinHandle<T>
+where
+    F: FnOnce() -> T + Send + 'static,
+    T: Send + 'static,
+{
+    eprintln!("warning: mocking won't work in `std::thread::spawn`ed threads by default. Use `std::mock::SharedMockData` if mocking is needed and it's safe to do so.");
+    std::thread::spawn(f)
+}
+
+pub struct Scope<'scope, 'env: 'scope> {
+    mock_data: super::mock::SharedMockData,
+    scope: &'scope std::thread::Scope<'scope, 'env>,
+}
+
+impl<'scope, 'env> Scope<'scope, 'env> {
+    pub fn spawn<F, T>(&self, f: F) -> ScopedJoinHandle<'scope, T>
+    where
+        F: FnOnce() -> T + Send + 'scope,
+        T: Send + 'scope,
+    {
+        let mock_data = self.mock_data.clone();
+        self.scope.spawn(move || {
+            // # Safety
+            // `thread::scope` guarantees that the mock data will outlive the thread.
+            unsafe { mock_data.set() };
+            f()
+        })
+    }
+}
+
+pub fn scope<'env, F, T>(f: F) -> T
+where
+    F: for<'scope> FnOnce(Scope<'scope, 'env>) -> T,
+{
+    let mock_data = super::mock::SharedMockData::new();
+    std::thread::scope(|scope| f(Scope { mock_data, scope }))
+}
diff --git a/toolkit/crashreporter/client/app/src/std/time.rs b/toolkit/crashreporter/client/app/src/std/time.rs
new file mode 100644
index 0000000000..5c351a7bcf
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/std/time.rs
@@ -0,0 +1,32 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use super::mock::{mock_key, MockKey};
+pub use std::time::{Duration, SystemTimeError};
+
+mock_key! {
+    pub struct MockCurrentTime => std::time::SystemTime
+}
+
+#[repr(transparent)]
+#[derive(Debug, Clone, Copy, PartialOrd, Ord, PartialEq, Eq)]
+pub struct SystemTime(pub(super) std::time::SystemTime);
+
+impl From<SystemTime> for ::time::OffsetDateTime {
+    fn from(t: SystemTime) -> Self {
+        t.0.into()
+    }
+}
+
+impl SystemTime {
+    pub const UNIX_EPOCH: SystemTime = SystemTime(std::time::SystemTime::UNIX_EPOCH);
+
+    pub fn now() -> Self {
+        MockCurrentTime.get(|t| SystemTime(*t))
+    }
+
+    pub fn duration_since(&self, earlier: Self) -> Result<Duration, SystemTimeError> {
+        self.0.duration_since(earlier.0)
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/test.rs b/toolkit/crashreporter/client/app/src/test.rs
new file mode 100644
index 0000000000..42d2334bca
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/test.rs
@@ -0,0 +1,1289 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Tests here mostly interact with the [test UI](crate::ui::test). As such, most tests read a bit
+//! more like integration tests than unit tests, testing the behavior of the application as a
+//! whole.
+
+use super::*;
+use crate::config::{test::MINIDUMP_PRUNE_SAVE_COUNT, Config};
+use crate::settings::Settings;
+use crate::std::{
+    ffi::OsString,
+    fs::{MockFS, MockFiles},
+    io::ErrorKind,
+    mock,
+    process::Command,
+    sync::{
+        atomic::{AtomicUsize, Ordering::Relaxed},
+        Arc,
+    },
+};
+use crate::ui::{self, test::model, ui_impl::Interact};
+
+/// A simple thread-safe counter which can be used in tests to mark that certain code paths were
+/// hit.
+#[derive(Clone, Default)]
+struct Counter(Arc<AtomicUsize>);
+
+impl Counter {
+    /// Create a new zero counter.
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Increment the counter.
+    pub fn inc(&self) {
+        self.0.fetch_add(1, Relaxed);
+    }
+
+    /// Get the current count.
+    pub fn count(&self) -> usize {
+        self.0.load(Relaxed)
+    }
+
+    /// Assert that the current count is 1.
+    pub fn assert_one(&self) {
+        assert_eq!(self.count(), 1);
+    }
+}
+
+/// Fluent wraps arguments with the unicode BiDi characters.
+struct FluentArg<T>(T);
+
+impl<T: std::fmt::Display> std::fmt::Display for FluentArg<T> {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        use crate::std::fmt::Write;
+        f.write_char('\u{2068}')?;
+        self.0.fmt(f)?;
+        f.write_char('\u{2069}')
+    }
+}
+
+/// Run a gui and interaction on separate threads.
+fn gui_interact<G, I, R>(gui: G, interact: I) -> R
+where
+    G: FnOnce() -> R,
+    I: FnOnce(Interact) + Send + 'static,
+{
+    let i = Interact::hook();
+    let handle = {
+        let i = i.clone();
+        ::std::thread::spawn(move || {
+            i.wait_for_ready();
+            interact(i);
+        })
+    };
+    let ret = gui();
+    // In case the gui failed before launching.
+    i.cancel();
+    handle.join().unwrap();
+    ret
+}
+
+const MOCK_MINIDUMP_EXTRA: &str = r#"{
+                            "Vendor": "FooCorp",
+                            "ProductName": "Bar",
+                            "ReleaseChannel": "release",
+                            "BuildID": "1234",
+                            "StackTraces": {
+                                "status": "OK"
+                            },
+                            "Version": "100.0",
+                            "ServerURL": "https://reports.example.com",
+                            "TelemetryServerURL": "https://telemetry.example.com",
+                            "TelemetryClientId": "telemetry_client",
+                            "TelemetrySessionId": "telemetry_session",
+                            "SomeNestedJson": { "foo": "bar" },
+                            "URL": "https://url.example.com"
+                        }"#;
+
+// Actual content doesn't matter, aside from the hash that is generated.
+const MOCK_MINIDUMP_FILE: &[u8] = &[1, 2, 3, 4];
+const MOCK_MINIDUMP_SHA256: &str =
+    "9f64a747e1b97f131fabb6b447296c9b6f0201e79fb3c5356e6c77e89b6a806a";
+macro_rules! current_date {
+    () => {
+        "2004-11-09"
+    };
+}
+const MOCK_CURRENT_DATE: &str = current_date!();
+const MOCK_CURRENT_TIME: &str = concat!(current_date!(), "T12:34:56Z");
+const MOCK_PING_UUID: uuid::Uuid = uuid::Uuid::nil();
+const MOCK_REMOTE_CRASH_ID: &str = "8cbb847c-def2-4f68-be9e-000000000000";
+
+fn current_datetime() -> time::OffsetDateTime {
+    time::OffsetDateTime::parse(
+        MOCK_CURRENT_TIME,
+        &time::format_description::well_known::Rfc3339,
+    )
+    .unwrap()
+}
+
+fn current_unix_time() -> i64 {
+    current_datetime().unix_timestamp()
+}
+
+fn current_system_time() -> ::std::time::SystemTime {
+    current_datetime().into()
+}
+
+/// A basic configuration which populates some necessary/useful fields.
+fn test_config() -> Config {
+    let mut cfg = Config::default();
+    cfg.data_dir = Some("data_dir".into());
+    cfg.events_dir = Some("events_dir".into());
+    cfg.ping_dir = Some("ping_dir".into());
+    cfg.dump_file = Some("minidump.dmp".into());
+    cfg.strings = lang::LanguageInfo::default().load_strings().ok();
+    cfg
+}
+
+/// A test fixture to make configuration, mocking, and assertions easier.
+struct GuiTest {
+    /// The configuration used in the test. Initialized to [`test_config`].
+    pub config: Config,
+    /// The mock builder used in the test, initialized with a basic set of mocked values to ensure
+    /// most things will work out of the box.
+    pub mock: mock::Builder,
+    /// The mocked filesystem, which can be used for mock setup and assertions after completion.
+    pub files: MockFiles,
+}
+
+impl GuiTest {
+    /// Create a new GuiTest with enough configured for the application to run
+    pub fn new() -> Self {
+        // Create a default set of files which allow successful operation.
+        let mock_files = MockFiles::new();
+        mock_files
+            .add_file_result(
+                "minidump.dmp",
+                Ok(MOCK_MINIDUMP_FILE.into()),
+                current_system_time(),
+            )
+            .add_file_result(
+                "minidump.extra",
+                Ok(MOCK_MINIDUMP_EXTRA.into()),
+                current_system_time(),
+            );
+
+        // Create a default mock environment which allows successful operation.
+        let mut mock = mock::builder();
+        mock.set(
+            Command::mock("work_dir/minidump-analyzer"),
+            Box::new(|_| Ok(crate::std::process::success_output())),
+        )
+        .set(
+            Command::mock("work_dir/pingsender"),
+            Box::new(|_| Ok(crate::std::process::success_output())),
+        )
+        .set(
+            Command::mock("curl"),
+            Box::new(|_| {
+                let mut output = crate::std::process::success_output();
+                output.stdout = format!("CrashID={MOCK_REMOTE_CRASH_ID}").into();
+                Ok(output)
+            }),
+        )
+        .set(MockFS, mock_files.clone())
+        .set(
+            crate::std::env::MockCurrentExe,
+            "work_dir/crashreporter".into(),
+        )
+        .set(crate::std::time::MockCurrentTime, current_system_time())
+        .set(mock::MockHook::new("ping_uuid"), MOCK_PING_UUID);
+
+        GuiTest {
+            config: test_config(),
+            mock,
+            files: mock_files,
+        }
+    }
+
+    /// Run the test as configured, using the given function to interact with the GUI.
+    ///
+    /// Returns the final result of the application logic.
+    pub fn try_run<F: FnOnce(Interact) + Send + 'static>(
+        &mut self,
+        interact: F,
+    ) -> anyhow::Result<bool> {
+        let GuiTest {
+            ref mut config,
+            ref mut mock,
+            ..
+        } = self;
+        let mut config = Arc::new(std::mem::take(config));
+
+        // Run the mock environment.
+        mock.run(move || gui_interact(move || try_run(&mut config), interact))
+    }
+
+    /// Run the test as configured, using the given function to interact with the GUI.
+    ///
+    /// Panics if the application logic returns an error (which would normally be displayed to the
+    /// user).
+    pub fn run<F: FnOnce(Interact) + Send + 'static>(&mut self, interact: F) {
+        if let Err(e) = self.try_run(interact) {
+            panic!(
+                "gui failure:{}",
+                e.chain().map(|e| format!("\n  {e}")).collect::<String>()
+            );
+        }
+    }
+
+    /// Get the file assertion helper.
+    pub fn assert_files(&self) -> AssertFiles {
+        AssertFiles {
+            data_dir: "data_dir".into(),
+            events_dir: "events_dir".into(),
+            inner: self.files.assert_files(),
+        }
+    }
+}
+
+/// A wrapper around the mock [`AssertFiles`](crate::std::fs::AssertFiles).
+///
+/// This implements higher-level assertions common across tests, but also supports the lower-level
+/// assertions (though those return the [`AssertFiles`](crate::std::fs::AssertFiles) reference so
+/// higher-level assertions must be chained first).
+struct AssertFiles {
+    data_dir: String,
+    events_dir: String,
+    inner: std::fs::AssertFiles,
+}
+
+impl AssertFiles {
+    fn data(&self, rest: &str) -> String {
+        format!("{}/{rest}", &self.data_dir)
+    }
+
+    fn events(&self, rest: &str) -> String {
+        format!("{}/{rest}", &self.events_dir)
+    }
+
+    /// Set the data dir if not the default.
+    pub fn set_data_dir<S: ToString>(&mut self, data_dir: S) -> &mut Self {
+        let data_dir = data_dir.to_string();
+        // Data dir should be relative to root.
+        self.data_dir = data_dir.trim_start_matches('/').to_string();
+        self
+    }
+
+    /// Ignore the generated log file.
+    pub fn ignore_log(&mut self) -> &mut Self {
+        self.inner.ignore(self.data("submit.log"));
+        self
+    }
+
+    /// Assert that the crash report was submitted according to the filesystem.
+    pub fn submitted(&mut self) -> &mut Self {
+        self.inner.check(
+            self.data(&format!("submitted/{MOCK_REMOTE_CRASH_ID}.txt")),
+            format!("Crash ID: {}\n", FluentArg(MOCK_REMOTE_CRASH_ID)),
+        );
+        self
+    }
+
+    /// Assert that the given settings where saved.
+    pub fn saved_settings(&mut self, settings: Settings) -> &mut Self {
+        self.inner.check(
+            self.data("crashreporter_settings.json"),
+            settings.to_string(),
+        );
+        self
+    }
+
+    /// Assert that a crash is pending according to the filesystem.
+    pub fn pending(&mut self) -> &mut Self {
+        let dmp = self.data("pending/minidump.dmp");
+        self.inner
+            .check(self.data("pending/minidump.extra"), MOCK_MINIDUMP_EXTRA)
+            .check_bytes(dmp, MOCK_MINIDUMP_FILE);
+        self
+    }
+
+    /// Assert that a crash ping was sent according to the filesystem.
+    pub fn ping(&mut self) -> &mut Self {
+        self.inner.check(
+            format!("ping_dir/{MOCK_PING_UUID}.json"),
+            serde_json::json! {{
+                "type": "crash",
+                "id": MOCK_PING_UUID,
+                "version": 4,
+                "creation_date": MOCK_CURRENT_TIME,
+                "client_id": "telemetry_client",
+                "payload": {
+                    "sessionId": "telemetry_session",
+                    "version": 1,
+                    "crashDate": MOCK_CURRENT_DATE,
+                    "crashTime": MOCK_CURRENT_TIME,
+                    "hasCrashEnvironment": true,
+                    "crashId": "minidump",
+                    "minidumpSha256Hash": MOCK_MINIDUMP_SHA256,
+                    "processType": "main",
+                    "stackTraces": {
+                        "status": "OK"
+                    },
+                    "metadata": {
+                        "BuildID": "1234",
+                        "ProductName": "Bar",
+                        "ReleaseChannel": "release",
+                    }
+                },
+                "application": {
+                    "vendor": "FooCorp",
+                    "name": "Bar",
+                    "buildId": "1234",
+                    "displayVersion": "",
+                    "platformVersion": "",
+                    "version": "100.0",
+                    "channel": "release"
+                }
+            }}
+            .to_string(),
+        );
+        self
+    }
+
+    /// Assert that a crash submission event was written with the given submission status.
+    pub fn submission_event(&mut self, success: bool) -> &mut Self {
+        self.inner.check(
+            self.events("minidump-submission"),
+            format!(
+                "crash.submission.1\n\
+                {}\n\
+                minidump\n\
+                {success}\n\
+                {}",
+                current_unix_time(),
+                if success { MOCK_REMOTE_CRASH_ID } else { "" }
+            ),
+        );
+        self
+    }
+}
+
+impl std::ops::Deref for AssertFiles {
+    type Target = std::fs::AssertFiles;
+    fn deref(&self) -> &Self::Target {
+        &self.inner
+    }
+}
+
+impl std::ops::DerefMut for AssertFiles {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.inner
+    }
+}
+
+#[test]
+fn error_dialog() {
+    gui_interact(
+        || {
+            let cfg = Config::default();
+            ui::error_dialog(&cfg, "an error occurred")
+        },
+        |interact| {
+            interact.element("close", |_style, b: &model::Button| b.click.fire(&()));
+        },
+    );
+}
+
+#[test]
+fn no_dump_file() {
+    let mut cfg = Arc::new(Config::default());
+    {
+        let cfg = Arc::get_mut(&mut cfg).unwrap();
+        cfg.strings = lang::LanguageInfo::default().load_strings().ok();
+    }
+    assert!(try_run(&mut cfg).is_err());
+    Arc::get_mut(&mut cfg).unwrap().auto_submit = true;
+    assert!(try_run(&mut cfg).is_ok());
+}
+
+#[test]
+fn minidump_analyzer_error() {
+    mock::builder()
+        .set(
+            Command::mock("work_dir/minidump-analyzer"),
+            Box::new(|_| Err(ErrorKind::NotFound.into())),
+        )
+        .set(
+            crate::std::env::MockCurrentExe,
+            "work_dir/crashreporter".into(),
+        )
+        .run(|| {
+            let cfg = test_config();
+            assert!(try_run(&mut Arc::new(cfg)).is_err());
+        });
+}
+
+#[test]
+fn no_extra_file() {
+    mock::builder()
+        .set(
+            Command::mock("work_dir/minidump-analyzer"),
+            Box::new(|_| Ok(crate::std::process::success_output())),
+        )
+        .set(
+            crate::std::env::MockCurrentExe,
+            "work_dir/crashreporter".into(),
+        )
+        .set(MockFS, {
+            let files = MockFiles::new();
+            files.add_file_result(
+                "minidump.extra",
+                Err(ErrorKind::NotFound.into()),
+                ::std::time::SystemTime::UNIX_EPOCH,
+            );
+            files
+        })
+        .run(|| {
+            let cfg = test_config();
+            assert!(try_run(&mut Arc::new(cfg)).is_err());
+        });
+}
+
+#[test]
+fn auto_submit() {
+    let mut test = GuiTest::new();
+    test.config.auto_submit = true;
+    // auto_submit should not do any GUI things, including creating the crashreporter_settings.json
+    // file.
+    test.mock.run(|| {
+        assert!(try_run(&mut Arc::new(std::mem::take(&mut test.config))).is_ok());
+    });
+    test.assert_files().ignore_log().submitted().pending();
+}
+
+#[test]
+fn restart() {
+    let mut test = GuiTest::new();
+    test.config.restart_command = Some("my_process".into());
+    test.config.restart_args = vec!["a".into(), "b".into()];
+    let ran_process = Counter::new();
+    let mock_ran_process = ran_process.clone();
+    test.mock.set(
+        Command::mock("my_process"),
+        Box::new(move |cmd| {
+            assert_eq!(cmd.args, &["a", "b"]);
+            mock_ran_process.inc();
+            Ok(crate::std::process::success_output())
+        }),
+    );
+    test.run(|interact| {
+        interact.element("restart", |_style, b: &model::Button| b.click.fire(&()));
+    });
+    test.assert_files()
+        .ignore_log()
+        .saved_settings(Settings::default())
+        .submitted()
+        .pending();
+    ran_process.assert_one();
+}
+
+#[test]
+fn no_restart_with_windows_error_reporting() {
+    let mut test = GuiTest::new();
+    test.config.restart_command = Some("my_process".into());
+    test.config.restart_args = vec!["a".into(), "b".into()];
+    // Add the "WindowsErrorReporting" key to the extra file
+    const MINIDUMP_EXTRA_CONTENTS: &str = r#"{
+                            "Vendor": "FooCorp",
+                            "ProductName": "Bar",
+                            "ReleaseChannel": "release",
+                            "BuildID": "1234",
+                            "StackTraces": {
+                                "status": "OK"
+                            },
+                            "Version": "100.0",
+                            "ServerURL": "https://reports.example.com",
+                            "TelemetryServerURL": "https://telemetry.example.com",
+                            "TelemetryClientId": "telemetry_client",
+                            "TelemetrySessionId": "telemetry_session",
+                            "SomeNestedJson": { "foo": "bar" },
+                            "URL": "https://url.example.com",
+                            "WindowsErrorReporting": 1
+                        }"#;
+    test.files = {
+        let mock_files = MockFiles::new();
+        mock_files
+            .add_file_result(
+                "minidump.dmp",
+                Ok(MOCK_MINIDUMP_FILE.into()),
+                current_system_time(),
+            )
+            .add_file_result(
+                "minidump.extra",
+                Ok(MINIDUMP_EXTRA_CONTENTS.into()),
+                current_system_time(),
+            );
+        test.mock.set(MockFS, mock_files.clone());
+        mock_files
+    };
+    let ran_process = Counter::new();
+    let mock_ran_process = ran_process.clone();
+    test.mock.set(
+        Command::mock("my_process"),
+        Box::new(move |cmd| {
+            assert_eq!(cmd.args, &["a", "b"]);
+            mock_ran_process.inc();
+            Ok(crate::std::process::success_output())
+        }),
+    );
+    test.run(|interact| {
+        interact.element("restart", |style, b: &model::Button| {
+            // Check that the button is hidden, and invoke the click anyway to ensure the process
+            // isn't restarted (the window will still be closed).
+            assert_eq!(style.visible.get(), false);
+            b.click.fire(&())
+        });
+    });
+    let mut assert_files = test.assert_files();
+    assert_files
+        .ignore_log()
+        .saved_settings(Settings::default())
+        .submitted();
+    {
+        let dmp = assert_files.data("pending/minidump.dmp");
+        let extra = assert_files.data("pending/minidump.extra");
+        assert_files
+            .check(extra, MINIDUMP_EXTRA_CONTENTS)
+            .check_bytes(dmp, MOCK_MINIDUMP_FILE);
+    }
+
+    assert_eq!(ran_process.count(), 0);
+}
+
+#[test]
+fn quit() {
+    let mut test = GuiTest::new();
+    test.run(|interact| {
+        interact.element("quit", |_style, b: &model::Button| b.click.fire(&()));
+    });
+    test.assert_files()
+        .ignore_log()
+        .saved_settings(Settings::default())
+        .submitted()
+        .pending();
+}
+
+#[test]
+fn delete_dump() {
+    let mut test = GuiTest::new();
+    test.config.delete_dump = true;
+    test.run(|interact| {
+        interact.element("quit", |_style, b: &model::Button| b.click.fire(&()));
+    });
+    test.assert_files()
+        .ignore_log()
+        .saved_settings(Settings::default())
+        .submitted();
+}
+
+#[test]
+fn no_submit() {
+    let mut test = GuiTest::new();
+    test.files.add_dir("data_dir").add_file(
+        "data_dir/crashreporter_settings.json",
+        Settings {
+            submit_report: true,
+            include_url: true,
+        }
+        .to_string(),
+    );
+    test.run(|interact| {
+        interact.element("send", |_style, c: &model::Checkbox| {
+            assert!(c.checked.get())
+        });
+        interact.element("include-url", |_style, c: &model::Checkbox| {
+            assert!(c.checked.get())
+        });
+        interact.element("send", |_style, c: &model::Checkbox| c.checked.set(false));
+        interact.element("include-url", |_style, c: &model::Checkbox| {
+            c.checked.set(false)
+        });
+
+        // When submission is unchecked, the following elements should be disabled.
+        interact.element("details", |style, _: &model::Button| {
+            assert!(!style.enabled.get());
+        });
+        interact.element("comment", |style, _: &model::TextBox| {
+            assert!(!style.enabled.get());
+        });
+        interact.element("include-url", |style, _: &model::Checkbox| {
+            assert!(!style.enabled.get());
+        });
+
+        interact.element("quit", |_style, b: &model::Button| b.click.fire(&()));
+    });
+    test.assert_files()
+        .ignore_log()
+        .saved_settings(Settings {
+            submit_report: false,
+            include_url: false,
+        })
+        .pending();
+}
+
+#[test]
+fn ping_and_event_files() {
+    let mut test = GuiTest::new();
+    test.files
+        .add_dir("ping_dir")
+        .add_dir("events_dir")
+        .add_file(
+            "events_dir/minidump",
+            "1\n\
+         12:34:56\n\
+         e0423878-8d59-4452-b82e-cad9c846836e\n\
+         {\"foo\":\"bar\"}",
+        );
+    test.run(|interact| {
+        interact.element("quit", |_style, b: &model::Button| b.click.fire(&()));
+    });
+    test.assert_files()
+        .ignore_log()
+        .saved_settings(Settings::default())
+        .submitted()
+        .pending()
+        .submission_event(true)
+        .ping()
+        .check(
+            "events_dir/minidump",
+            format!(
+                "1\n\
+                12:34:56\n\
+                e0423878-8d59-4452-b82e-cad9c846836e\n\
+                {}",
+                serde_json::json! {{
+                    "foo": "bar",
+                    "MinidumpSha256Hash": MOCK_MINIDUMP_SHA256,
+                    "CrashPingUUID": MOCK_PING_UUID,
+                    "StackTraces": { "status": "OK" }
+                }}
+            ),
+        );
+}
+
+#[test]
+fn pingsender_failure() {
+    let mut test = GuiTest::new();
+    test.mock.set(
+        Command::mock("work_dir/pingsender"),
+        Box::new(|_| Err(ErrorKind::NotFound.into())),
+    );
+    test.files
+        .add_dir("ping_dir")
+        .add_dir("events_dir")
+        .add_file(
+            "events_dir/minidump",
+            "1\n\
+         12:34:56\n\
+         e0423878-8d59-4452-b82e-cad9c846836e\n\
+         {\"foo\":\"bar\"}",
+        );
+    test.run(|interact| {
+        interact.element("quit", |_style, b: &model::Button| b.click.fire(&()));
+    });
+    test.assert_files()
+        .ignore_log()
+        .saved_settings(Settings::default())
+        .submitted()
+        .pending()
+        .submission_event(true)
+        .ping()
+        .check(
+            "events_dir/minidump",
+            format!(
+                "1\n\
+                12:34:56\n\
+                e0423878-8d59-4452-b82e-cad9c846836e\n\
+                {}",
+                serde_json::json! {{
+                    "foo": "bar",
+                    "MinidumpSha256Hash": MOCK_MINIDUMP_SHA256,
+                    // No crash ping UUID since pingsender fails
+                    "StackTraces": { "status": "OK" }
+                }}
+            ),
+        );
+}
+
+#[test]
+fn eol_version() {
+    let mut test = GuiTest::new();
+    test.files
+        .add_dir("data_dir")
+        .add_file("data_dir/EndOfLife100.0", "");
+    // Should fail before opening the gui
+    let result = test.try_run(|_| ());
+    assert_eq!(
+        result.expect_err("should fail on EOL version").to_string(),
+        "Version end of life: crash reports are no longer accepted."
+    );
+    test.assert_files()
+        .ignore_log()
+        .pending()
+        .ignore("data_dir/EndOfLife100.0");
+}
+
+#[test]
+fn details_window() {
+    let mut test = GuiTest::new();
+    test.run(|interact| {
+        let details_visible = || {
+            interact.window("crash-details-window", |style, _w: &model::Window| {
+                style.visible.get()
+            })
+        };
+        assert_eq!(details_visible(), false);
+        interact.element("details", |_style, b: &model::Button| b.click.fire(&()));
+        assert_eq!(details_visible(), true);
+        let details_text = loop {
+            let v = interact.element("details-text", |_style, t: &model::TextBox| t.content.get());
+            if v == "Loading…" {
+                // Wait for the details to be populated.
+                std::thread::sleep(std::time::Duration::from_millis(50));
+                continue;
+            } else {
+                break v;
+            }
+        };
+        interact.element("close-details", |_style, b: &model::Button| b.click.fire(&()));
+        assert_eq!(details_visible(), false);
+        interact.element("quit", |_style, b: &model::Button| b.click.fire(&()));
+        assert_eq!(details_text,
+            "BuildID: 1234\n\
+             ProductName: Bar\n\
+             ReleaseChannel: release\n\
+             SomeNestedJson: {\"foo\":\"bar\"}\n\
+             SubmittedFrom: Client\n\
+             TelemetryClientId: telemetry_client\n\
+             TelemetryServerURL: https://telemetry.example.com\n\
+             TelemetrySessionId: telemetry_session\n\
+             Throttleable: 1\n\
+             Vendor: FooCorp\n\
+             Version: 100.0\n\
+             This report also contains technical information about the state of the application when it crashed.\n"
+        );
+    });
+}
+
+#[test]
+fn data_dir_default() {
+    let mut test = GuiTest::new();
+    test.config.data_dir = None;
+    test.run(|interact| {
+        interact.element("quit", |_style, b: &model::Button| b.click.fire(&()));
+    });
+    test.assert_files()
+        .set_data_dir("data_dir/FooCorp/Bar/Crash Reports")
+        .ignore_log()
+        .saved_settings(Settings::default())
+        .submitted()
+        .pending();
+}
+
+#[test]
+fn include_url() {
+    for setting in [false, true] {
+        let mut test = GuiTest::new();
+        test.files.add_dir("data_dir").add_file(
+            "data_dir/crashreporter_settings.json",
+            Settings {
+                submit_report: true,
+                include_url: setting,
+            }
+            .to_string(),
+        );
+        test.mock
+            .set(
+                Command::mock("curl"),
+                Box::new(|_| Err(std::io::ErrorKind::NotFound.into())),
+            )
+            .set(
+                net::report::MockLibCurl,
+                Box::new(move |report| {
+                    assert_eq!(
+                        report.extra.get("URL").and_then(|v| v.as_str()),
+                        setting.then_some("https://url.example.com")
+                    );
+                    Ok(Ok(format!("CrashID={MOCK_REMOTE_CRASH_ID}")))
+                }),
+            );
+        test.run(|interact| {
+            interact.element("quit", |_style, b: &model::Button| b.click.fire(&()));
+        });
+    }
+}
+
+#[test]
+fn comment() {
+    const COMMENT: &str = "My program crashed";
+
+    for set_comment in [false, true] {
+        let invoked = Counter::new();
+        let mock_invoked = invoked.clone();
+        let mut test = GuiTest::new();
+        test.mock
+            .set(
+                Command::mock("curl"),
+                Box::new(|_| Err(std::io::ErrorKind::NotFound.into())),
+            )
+            .set(
+                net::report::MockLibCurl,
+                Box::new(move |report| {
+                    mock_invoked.inc();
+                    assert_eq!(
+                        report.extra.get("Comments").and_then(|v| v.as_str()),
+                        set_comment.then_some(COMMENT)
+                    );
+                    Ok(Ok(format!("CrashID={MOCK_REMOTE_CRASH_ID}")))
+                }),
+            );
+        test.run(move |interact| {
+            if set_comment {
+                interact.element("comment", |_style, c: &model::TextBox| {
+                    c.content.set(COMMENT.into())
+                });
+            }
+            interact.element("quit", |_style, b: &model::Button| b.click.fire(&()));
+        });
+
+        invoked.assert_one();
+    }
+}
+
+#[test]
+fn curl_binary() {
+    let mut test = GuiTest::new();
+    test.files.add_file("minidump.memory.json.gz", "");
+    let ran_process = Counter::new();
+    let mock_ran_process = ran_process.clone();
+    test.mock.set(
+        Command::mock("curl"),
+        Box::new(move |cmd| {
+            if cmd.spawning {
+                return Ok(crate::std::process::success_output());
+            }
+
+            // Curl strings need backslashes escaped.
+            let curl_escaped_separator = if std::path::MAIN_SEPARATOR == '\\' {
+                "\\\\"
+            } else {
+                std::path::MAIN_SEPARATOR_STR
+            };
+
+            let expected_args: Vec<OsString> = [
+                "--user-agent",
+                net::report::USER_AGENT,
+                "--form",
+                "extra=@-;filename=extra.json;type=application/json",
+                "--form",
+                &format!(
+                    "upload_file_minidump=@\"data_dir{0}pending{0}minidump.dmp\"",
+                    curl_escaped_separator
+                ),
+                "--form",
+                &format!(
+                    "memory_report=@\"data_dir{0}pending{0}minidump.memory.json.gz\"",
+                    curl_escaped_separator
+                ),
+                "https://reports.example.com",
+            ]
+            .into_iter()
+            .map(Into::into)
+            .collect();
+            assert_eq!(cmd.args, expected_args);
+            let mut output = crate::std::process::success_output();
+            output.stdout = format!("CrashID={MOCK_REMOTE_CRASH_ID}").into();
+            mock_ran_process.inc();
+            Ok(output)
+        }),
+    );
+    test.run(|interact| {
+        interact.element("quit", |_style, b: &model::Button| b.click.fire(&()));
+    });
+
+    ran_process.assert_one();
+}
+
+#[test]
+fn curl_library() {
+    let invoked = Counter::new();
+    let mock_invoked = invoked.clone();
+    let mut test = GuiTest::new();
+    test.mock
+        .set(
+            Command::mock("curl"),
+            Box::new(|_| Err(std::io::ErrorKind::NotFound.into())),
+        )
+        .set(
+            net::report::MockLibCurl,
+            Box::new(move |_| {
+                mock_invoked.inc();
+                Ok(Ok(format!("CrashID={MOCK_REMOTE_CRASH_ID}")))
+            }),
+        );
+    test.run(|interact| {
+        interact.element("quit", |_style, b: &model::Button| b.click.fire(&()));
+    });
+    invoked.assert_one();
+}
+
+#[test]
+fn report_not_sent() {
+    let mut test = GuiTest::new();
+    test.files.add_dir("events_dir");
+    test.mock
+        .set(
+            Command::mock("curl"),
+            Box::new(|_| Err(std::io::ErrorKind::NotFound.into())),
+        )
+        .set(
+            net::report::MockLibCurl,
+            Box::new(move |_| Err(std::io::ErrorKind::NotFound.into())),
+        );
+    test.run(|interact| {
+        interact.element("quit", |_style, b: &model::Button| b.click.fire(&()));
+    });
+
+    test.assert_files()
+        .ignore_log()
+        .saved_settings(Settings::default())
+        .submission_event(false)
+        .pending();
+}
+
+#[test]
+fn report_response_failed() {
+    let mut test = GuiTest::new();
+    test.files.add_dir("events_dir");
+    test.mock
+        .set(
+            Command::mock("curl"),
+            Box::new(|_| Err(std::io::ErrorKind::NotFound.into())),
+        )
+        .set(
+            net::report::MockLibCurl,
+            Box::new(move |_| Ok(Err(std::io::ErrorKind::NotFound.into()))),
+        );
+    test.run(|interact| {
+        interact.element("quit", |_style, b: &model::Button| b.click.fire(&()));
+    });
+
+    test.assert_files()
+        .ignore_log()
+        .saved_settings(Settings::default())
+        .submission_event(false)
+        .pending();
+}
+
+#[test]
+fn response_indicates_discarded() {
+    let mut test = GuiTest::new();
+    // A response indicating discarded triggers a prune of the directory containing the minidump.
+    // Since there is one more minidump (the main one, minidump.dmp), pruning should keep all but
+    // the first 3, which will be the oldest.
+    const SHOULD_BE_PRUNED: usize = 3;
+
+    for i in 0..MINIDUMP_PRUNE_SAVE_COUNT + SHOULD_BE_PRUNED - 1 {
+        test.files.add_dir("data_dir/pending").add_file_result(
+            format!("data_dir/pending/minidump{i}.dmp"),
+            Ok("contents".into()),
+            ::std::time::SystemTime::UNIX_EPOCH + ::std::time::Duration::from_secs(1234 + i as u64),
+        );
+        if i % 2 == 0 {
+            test.files
+                .add_file(format!("data_dir/pending/minidump{i}.extra"), "{}");
+        }
+        if i % 5 == 0 {
+            test.files
+                .add_file(format!("data_dir/pending/minidump{i}.memory.json.gz"), "{}");
+        }
+    }
+    test.mock.set(
+        Command::mock("curl"),
+        Box::new(|_| {
+            let mut output = crate::std::process::success_output();
+            output.stdout = format!("CrashID={MOCK_REMOTE_CRASH_ID}\nDiscarded=1").into();
+            Ok(output)
+        }),
+    );
+    test.run(|interact| {
+        interact.element("quit", |_style, b: &model::Button| b.click.fire(&()));
+    });
+
+    let mut assert_files = test.assert_files();
+    assert_files
+        .ignore_log()
+        .saved_settings(Settings::default())
+        .pending();
+    for i in SHOULD_BE_PRUNED..MINIDUMP_PRUNE_SAVE_COUNT + SHOULD_BE_PRUNED - 1 {
+        assert_files.check_exists(format!("data_dir/pending/minidump{i}.dmp"));
+        if i % 2 == 0 {
+            assert_files.check_exists(format!("data_dir/pending/minidump{i}.extra"));
+        }
+        if i % 5 == 0 {
+            assert_files.check_exists(format!("data_dir/pending/minidump{i}.memory.json.gz"));
+        }
+    }
+}
+
+#[test]
+fn response_view_url() {
+    let mut test = GuiTest::new();
+    test.mock.set(
+        Command::mock("curl"),
+        Box::new(|_| {
+            let mut output = crate::std::process::success_output();
+            output.stdout =
+                format!("CrashID={MOCK_REMOTE_CRASH_ID}\nViewURL=https://foo.bar.example").into();
+            Ok(output)
+        }),
+    );
+    test.run(|interact| {
+        interact.element("quit", |_style, b: &model::Button| b.click.fire(&()));
+    });
+
+    test.assert_files()
+        .ignore_log()
+        .saved_settings(Settings::default())
+        .pending()
+        .check(
+            format!("data_dir/submitted/{MOCK_REMOTE_CRASH_ID}.txt"),
+            format!(
+                "\
+                Crash ID: {}\n\
+                You can view details of this crash at {}.\n",
+                FluentArg(MOCK_REMOTE_CRASH_ID),
+                FluentArg("https://foo.bar.example")
+            ),
+        );
+}
+
+#[test]
+fn response_stop_sending_reports() {
+    let mut test = GuiTest::new();
+    test.mock.set(
+        Command::mock("curl"),
+        Box::new(|_| {
+            let mut output = crate::std::process::success_output();
+            output.stdout =
+                format!("CrashID={MOCK_REMOTE_CRASH_ID}\nStopSendingReportsFor=100.0").into();
+            Ok(output)
+        }),
+    );
+    test.run(|interact| {
+        interact.element("quit", |_style, b: &model::Button| b.click.fire(&()));
+    });
+
+    test.assert_files()
+        .ignore_log()
+        .saved_settings(Settings::default())
+        .submitted()
+        .pending()
+        .check_exists("data_dir/EndOfLife100.0");
+}
+
+/// A real temporary directory in the host filesystem.
+///
+/// The directory is guaranteed to be unique to the test suite process (in case of crash, it can be
+/// inspected).
+///
+/// When dropped, the directory is deleted.
+struct TempDir {
+    path: ::std::path::PathBuf,
+}
+
+impl TempDir {
+    /// Create a new directory with the given identifying name.
+    ///
+    /// The name should be unique to deconflict amongst concurrent tests.
+    pub fn new(name: &str) -> Self {
+        let path = ::std::env::temp_dir().join(format!(
+            "{}-test-{}-{name}",
+            env!("CARGO_PKG_NAME"),
+            std::process::id()
+        ));
+        ::std::fs::create_dir_all(&path).unwrap();
+        TempDir { path }
+    }
+
+    /// Get the temporary directory path.
+    pub fn path(&self) -> &::std::path::Path {
+        &self.path
+    }
+}
+
+impl Drop for TempDir {
+    fn drop(&mut self) {
+        // Best-effort removal, ignore errors.
+        let _ = ::std::fs::remove_dir_all(&self.path);
+    }
+}
+
+/// A mock crash report server.
+///
+/// When dropped, the server is shutdown.
+struct TestCrashReportServer {
+    addr: ::std::net::SocketAddr,
+    shutdown_and_thread: Option<(
+        tokio::sync::oneshot::Sender<()>,
+        std::thread::JoinHandle<()>,
+    )>,
+}
+
+impl TestCrashReportServer {
+    /// Create and start a mock crash report server on an ephemeral port, returning a handle to the
+    /// server.
+    pub fn run() -> Self {
+        let (shutdown, rx) = tokio::sync::oneshot::channel();
+
+        use warp::Filter;
+
+        let submit = warp::path("submit")
+            .and(warp::filters::method::post())
+            .and(warp::filters::header::header("content-type"))
+            .and(warp::filters::body::bytes())
+            .and_then(|content_type: String, body: bytes::Bytes| async move {
+                let Some(boundary) = content_type.strip_prefix("multipart/form-data; boundary=")
+                else {
+                    return Err(warp::reject());
+                };
+
+                let body = String::from_utf8_lossy(&*body).to_owned();
+
+                for part in body.split(&format!("--{boundary}")).skip(1) {
+                    if part == "--\r\n" {
+                        break;
+                    }
+
+                    let (_headers, _data) = part.split_once("\r\n\r\n").unwrap_or(("", part));
+                    // TODO validate parts
+                }
+                Ok(format!("CrashID={MOCK_REMOTE_CRASH_ID}"))
+            });
+
+        let (addr_channel_tx, addr_channel_rx) = std::sync::mpsc::sync_channel(0);
+
+        let thread = ::std::thread::spawn(move || {
+            let rt = tokio::runtime::Builder::new_current_thread()
+                .enable_all()
+                .build()
+                .expect("failed to create tokio runtime");
+            let _guard = rt.enter();
+
+            let (addr, server) =
+                warp::serve(submit).bind_with_graceful_shutdown(([127, 0, 0, 1], 0), async move {
+                    rx.await.ok();
+                });
+
+            addr_channel_tx.send(addr).unwrap();
+
+            rt.block_on(server)
+        });
+
+        let addr = addr_channel_rx.recv().unwrap();
+
+        TestCrashReportServer {
+            addr,
+            shutdown_and_thread: Some((shutdown, thread)),
+        }
+    }
+
+    /// Get the url to which to submit crash reports for this mocked server.
+    pub fn submit_url(&self) -> String {
+        format!("http://{}/submit", self.addr)
+    }
+}
+
+impl Drop for TestCrashReportServer {
+    fn drop(&mut self) {
+        let (shutdown, thread) = self.shutdown_and_thread.take().unwrap();
+        let _ = shutdown.send(());
+        thread.join().unwrap();
+    }
+}
+
+#[test]
+fn real_curl_binary() {
+    if ::std::process::Command::new("curl").output().is_err() {
+        eprintln!("no curl binary; skipping real_curl_binary test");
+        return;
+    }
+
+    let server = TestCrashReportServer::run();
+
+    let mut test = GuiTest::new();
+    test.mock.set(
+        Command::mock("curl"),
+        Box::new(|cmd| cmd.output_from_real_command()),
+    );
+    test.config.report_url = Some(server.submit_url().into());
+    test.config.delete_dump = true;
+
+    // We need the dump file to actually exist since the curl binary is passed the file path.
+    // The dump file needs to exist at the pending dir location.
+
+    let tempdir = TempDir::new("real_curl_binary");
+    let data_dir = tempdir.path().to_owned();
+    let pending_dir = data_dir.join("pending");
+    test.config.data_dir = Some(data_dir.clone().into());
+    ::std::fs::create_dir_all(&pending_dir).unwrap();
+    let dump_file = pending_dir.join("minidump.dmp");
+    ::std::fs::write(&dump_file, MOCK_MINIDUMP_FILE).unwrap();
+
+    test.run(|interact| {
+        interact.element("quit", |_style, b: &model::Button| b.click.fire(&()));
+    });
+
+    test.assert_files()
+        .set_data_dir(data_dir.display())
+        .ignore_log()
+        .saved_settings(Settings::default())
+        .submitted();
+}
+
+#[test]
+fn real_curl_library() {
+    if !crate::net::can_load_libcurl() {
+        eprintln!("no libcurl; skipping real_libcurl test");
+        return;
+    }
+
+    let server = TestCrashReportServer::run();
+
+    let mut test = GuiTest::new();
+    test.mock
+        .set(
+            Command::mock("curl"),
+            Box::new(|_| Err(std::io::ErrorKind::NotFound.into())),
+        )
+        .set(mock::MockHook::new("use_system_libcurl"), true);
+    test.config.report_url = Some(server.submit_url().into());
+    test.config.delete_dump = true;
+
+    // We need the dump file to actually exist since libcurl is passed the file path.
+    // The dump file needs to exist at the pending dir location.
+
+    let tempdir = TempDir::new("real_libcurl");
+    let data_dir = tempdir.path().to_owned();
+    let pending_dir = data_dir.join("pending");
+    test.config.data_dir = Some(data_dir.clone().into());
+    ::std::fs::create_dir_all(&pending_dir).unwrap();
+    let dump_file = pending_dir.join("minidump.dmp");
+    ::std::fs::write(&dump_file, MOCK_MINIDUMP_FILE).unwrap();
+
+    test.run(|interact| {
+        interact.element("quit", |_style, b: &model::Button| b.click.fire(&()));
+    });
+
+    test.assert_files()
+        .set_data_dir(data_dir.display())
+        .ignore_log()
+        .saved_settings(Settings::default())
+        .submitted();
+}
diff --git a/toolkit/crashreporter/client/app/src/thread_bound.rs b/toolkit/crashreporter/client/app/src/thread_bound.rs
new file mode 100644
index 0000000000..28095f42f4
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/thread_bound.rs
@@ -0,0 +1,41 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Encapsulate thread-bound values in a safe manner.
+//!
+//! This allows non-`Send`/`Sync` values to be transferred across thread boundaries, checking at
+//! runtime at access sites whether it is safe to use them.
+
+pub struct ThreadBound<T> {
+    data: T,
+    origin: std::thread::ThreadId,
+}
+
+impl<T: Default> Default for ThreadBound<T> {
+    fn default() -> Self {
+        ThreadBound::new(Default::default())
+    }
+}
+
+impl<T> ThreadBound<T> {
+    pub fn new(data: T) -> Self {
+        ThreadBound {
+            data,
+            origin: std::thread::current().id(),
+        }
+    }
+
+    pub fn borrow(&self) -> &T {
+        assert!(
+            std::thread::current().id() == self.origin,
+            "unsafe access to thread-bound value"
+        );
+        &self.data
+    }
+}
+
+// # Safety
+// Access to the inner value is only permitted on the originating thread.
+unsafe impl<T> Send for ThreadBound<T> {}
+unsafe impl<T> Sync for ThreadBound<T> {}
diff --git a/toolkit/crashreporter/client/app/src/ui/crashreporter.png b/toolkit/crashreporter/client/app/src/ui/crashreporter.png
new file mode 100644
index 0000000000..5e68bac17c
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/ui/crashreporter.png
diff --git a/toolkit/crashreporter/client/app/src/ui/gtk.rs b/toolkit/crashreporter/client/app/src/ui/gtk.rs
new file mode 100644
index 0000000000..a76f99b0bd
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/ui/gtk.rs
@@ -0,0 +1,841 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use super::model::{self, Alignment, Application, Element};
+use crate::std::{
+    cell::RefCell,
+    ffi::{c_char, CString},
+    rc::Rc,
+    sync::atomic::{AtomicBool, Ordering::Relaxed},
+};
+use crate::{
+    data::{Event, Property, Synchronized},
+    std,
+};
+
+/// Create a `std::ffi::CStr` directly from a literal string.
+///
+/// The argument is an `expr` rather than `literal` so that other macros can be used (such as
+/// `stringify!`).
+macro_rules! cstr {
+    ( $str:expr ) => {
+        #[allow(unused_unsafe)]
+        unsafe { std::ffi::CStr::from_bytes_with_nul_unchecked(concat!($str, "\0").as_bytes()) }
+            .as_ptr()
+    };
+}
+
+/// A GTK+ UI implementation.
+#[derive(Default)]
+pub struct UI {
+    running: AtomicBool,
+}
+
+impl UI {
+    pub fn run_loop(&self, app: Application) {
+        unsafe {
+            let stream = gtk::g_memory_input_stream_new_from_data(
+                super::icon::PNG_DATA.as_ptr() as _,
+                // unwrap() because the PNG_DATA length will be well within gssize limits (32-bit
+                // at the smallest).
+                super::icon::PNG_DATA.len().try_into().unwrap(),
+                None,
+            );
+            let icon_pixbuf =
+                gtk::gdk_pixbuf_new_from_stream(stream, std::ptr::null_mut(), std::ptr::null_mut());
+            gtk::g_object_unref(stream as _);
+
+            gtk::gtk_window_set_default_icon(icon_pixbuf);
+
+            let app_ptr = gtk::gtk_application_new(
+                std::ptr::null(),
+                gtk::GApplicationFlags_G_APPLICATION_FLAGS_NONE,
+            );
+            gtk::g_signal_connect_data(
+                app_ptr as *mut _,
+                cstr!("activate"),
+                Some(std::mem::transmute(
+                    render_application
+                        as for<'a> unsafe extern "C" fn(*mut gtk::GtkApplication, &'a Application),
+                )),
+                &app as *const Application as *mut Application as _,
+                None,
+                0,
+            );
+            self.running.store(true, Relaxed);
+            gtk::g_application_run(app_ptr as *mut gtk::GApplication, 0, std::ptr::null_mut());
+            self.running.store(false, Relaxed);
+            gtk::g_object_unref(app_ptr as *mut _);
+            gtk::g_object_unref(icon_pixbuf as _);
+        }
+    }
+
+    pub fn invoke(&self, f: model::InvokeFn) {
+        if !self.running.load(Relaxed) {
+            log::debug!("ignoring `invoke` as main loop isn't running");
+            return;
+        }
+        type BoxedData = Option<model::InvokeFn>;
+
+        unsafe extern "C" fn call(ptr: gtk::gpointer) -> gtk::gboolean {
+            let f: &mut BoxedData = ToPointer::from_ptr(ptr as _);
+            f.take().unwrap()();
+            false.into()
+        }
+
+        unsafe extern "C" fn drop(ptr: gtk::gpointer) {
+            let _: Box<BoxedData> = ToPointer::from_ptr(ptr as _);
+        }
+
+        let data: Box<BoxedData> = Box::new(Some(f));
+
+        unsafe {
+            let main_context = gtk::g_main_context_default();
+            gtk::g_main_context_invoke_full(
+                main_context,
+                0, // G_PRIORITY_DEFAULT
+                Some(call as unsafe extern "C" fn(gtk::gpointer) -> gtk::gboolean),
+                data.to_ptr() as _,
+                Some(drop as unsafe extern "C" fn(gtk::gpointer)),
+            );
+        }
+    }
+}
+
+/// Types that can be converted to and from a pointer.
+///
+/// These types must be sized to avoid fat pointers (i.e., the pointers must be FFI-compatible, the
+/// same size as usize).
+trait ToPointer: Sized {
+    fn to_ptr(self) -> *mut ();
+    /// # Safety
+    /// The caller must ensure that the pointer was created as the result of `to_ptr` on the same
+    /// or a compatible type, and that the data is still valid.
+    unsafe fn from_ptr(ptr: *mut ()) -> Self;
+}
+
+/// Types that can be attached to a GLib object to be dropped when the widget is dropped.
+trait DropWithObject: Sized {
+    fn drop_with_object(self, object: *mut gtk::GObject);
+    fn drop_with_widget(self, widget: *mut gtk::GtkWidget) {
+        self.drop_with_object(widget as *mut _);
+    }
+
+    fn set_data(self, object: *mut gtk::GObject, key: *const c_char);
+}
+
+impl<T: ToPointer> DropWithObject for T {
+    fn drop_with_object(self, object: *mut gtk::GObject) {
+        unsafe extern "C" fn free_ptr<T: ToPointer>(
+            ptr: gtk::gpointer,
+            _object: *mut gtk::GObject,
+        ) {
+            drop(T::from_ptr(ptr as *mut ()));
+        }
+        unsafe { gtk::g_object_weak_ref(object, Some(free_ptr::<T>), self.to_ptr() as *mut _) };
+    }
+
+    fn set_data(self, object: *mut gtk::GObject, key: *const c_char) {
+        unsafe extern "C" fn free_ptr<T: ToPointer>(ptr: gtk::gpointer) {
+            drop(T::from_ptr(ptr as *mut ()));
+        }
+        unsafe {
+            gtk::g_object_set_data_full(object, key, self.to_ptr() as *mut _, Some(free_ptr::<T>))
+        };
+    }
+}
+
+impl ToPointer for CString {
+    fn to_ptr(self) -> *mut () {
+        self.into_raw() as _
+    }
+
+    unsafe fn from_ptr(ptr: *mut ()) -> Self {
+        CString::from_raw(ptr as *mut c_char)
+    }
+}
+
+impl<T> ToPointer for Rc<T> {
+    fn to_ptr(self) -> *mut () {
+        Rc::into_raw(self) as *mut T as *mut ()
+    }
+
+    unsafe fn from_ptr(ptr: *mut ()) -> Self {
+        Rc::from_raw(ptr as *mut T as *const T)
+    }
+}
+
+impl<T> ToPointer for Box<T> {
+    fn to_ptr(self) -> *mut () {
+        Box::into_raw(self) as _
+    }
+
+    unsafe fn from_ptr(ptr: *mut ()) -> Self {
+        Box::from_raw(ptr as _)
+    }
+}
+
+impl<T: Sized> ToPointer for &mut T {
+    fn to_ptr(self) -> *mut () {
+        self as *mut T as _
+    }
+
+    unsafe fn from_ptr(ptr: *mut ()) -> Self {
+        &mut *(ptr as *mut T)
+    }
+}
+
+/// Connect a GTK+ object signal to a function, providing an additional context value (by
+/// reference).
+macro_rules! connect_signal {
+    ( object $object:expr ; with $with:expr ;
+      signal $name:ident ($target:ident : &$type:ty $(, $argname:ident : $argtype:ty )* ) $( -> $ret:ty )? $body:block
+    ) => {{
+        unsafe extern "C" fn $name($($argname : $argtype ,)* $target: &$type) $( -> $ret )? $body
+        #[allow(unused_unsafe)]
+        unsafe {
+            gtk::g_signal_connect_data(
+                $object as *mut _,
+                cstr!(stringify!($name)),
+                Some(std::mem::transmute(
+                    $name
+                        as for<'a> unsafe extern "C" fn(
+                            $($argtype,)*
+                            &'a $type,
+                        ) $( -> $ret )?,
+                )),
+                $with as *const $type as *mut $type as _,
+                None,
+                0,
+            );
+        }
+    }};
+}
+
+/// Bind a read only (from the renderer perspective) property to a widget.
+///
+/// The `set` function is called initially and when the property value changes.
+macro_rules! property_read_only {
+    ( property $property:expr ;
+      fn set( $name:ident : & $type:ty ) $setbody:block
+    ) => {{
+        let prop: &Property<$type> = $property;
+        match prop {
+            Property::Static($name) => $setbody,
+            Property::Binding(v) => {
+                {
+                    let $name = v.borrow();
+                    $setbody
+                }
+                v.on_change(move |$name| $setbody);
+            }
+            Property::ReadOnly(_) => (),
+        }
+    }};
+}
+
+/// Bind a read/write property to a widget signal.
+///
+/// This currently only allows signals which are of the form
+/// `void(*)(SomeGtkObject*, gpointer user_data)`.
+macro_rules! property_with_signal {
+    ( object $object:expr ; property $property:expr ; signal $signame:ident ;
+      fn set( $name:ident : & $type:ty ) $setbody:block
+      fn get( $getobj:ident : $gettype:ty ) -> $result:ty $getbody:block
+    ) => {{
+        let prop: &Property<$type> = $property;
+        match prop {
+            Property::Static($name) => $setbody,
+            Property::Binding(v) => {
+                {
+                    let $name = v.borrow();
+                    $setbody
+                }
+                let changing = Rc::new(RefCell::new(false));
+                struct SignalData {
+                    changing: Rc<RefCell<bool>>,
+                    value: Synchronized<$result>,
+                }
+                let signal_data = Box::new(SignalData {
+                    changing: changing.clone(),
+                    value: v.clone(),
+                });
+                v.on_change(move |$name| {
+                    if !*changing.borrow() {
+                        *changing.borrow_mut() = true;
+                        $setbody;
+                        *changing.borrow_mut() = false;
+                    }
+                });
+                connect_signal! {
+                    object $object;
+                    with signal_data.as_ref();
+                    signal $signame(signal_data: &SignalData, $getobj: $gettype) {
+                        let new_value = (|| $getbody)();
+                        if !*signal_data.changing.borrow() {
+                            *signal_data.changing.borrow_mut() = true;
+                            *signal_data.value.borrow_mut() = new_value;
+                            *signal_data.changing.borrow_mut() = false;
+                        }
+                    }
+                }
+                signal_data.drop_with_object($object as _);
+            }
+            Property::ReadOnly(v) => {
+                v.register(move |target: &mut $result| {
+                    let $getobj: $gettype = $object as _;
+                    *target = (|| $getbody)();
+                });
+            }
+        }
+    }};
+}
+
+unsafe extern "C" fn render_application(app_ptr: *mut gtk::GtkApplication, app: &Application) {
+    unsafe {
+        gtk::gtk_widget_set_default_direction(if app.rtl {
+            gtk::GtkTextDirection_GTK_TEXT_DIR_RTL
+        } else {
+            gtk::GtkTextDirection_GTK_TEXT_DIR_LTR
+        });
+    }
+    for window in &app.windows {
+        let window_ptr = render_window(&window.element_type);
+        let style = &window.style;
+
+        // Set size before applying style (since the style will set the visibility and show the
+        // window). Note that we take the size request as an initial size here.
+        //
+        // `gtk_window_set_default_size` doesn't work; it resizes to the size request of the inner
+        // labels (instead of wrapping them) since it doesn't know how small they should be (that's
+        // dictated by the window size!).
+        unsafe {
+            gtk::gtk_window_resize(
+                window_ptr as _,
+                style
+                    .horizontal_size_request
+                    .map(|v| v as i32)
+                    .unwrap_or(-1),
+                style.vertical_size_request.map(|v| v as i32).unwrap_or(-1),
+            );
+        }
+
+        apply_style(window_ptr, style);
+        unsafe {
+            gtk::gtk_application_add_window(app_ptr, window_ptr as *mut _);
+        }
+    }
+}
+
+fn render(element: &Element) -> Option<*mut gtk::GtkWidget> {
+    let widget = render_element_type(&element.element_type)?;
+    apply_style(widget, &element.style);
+    Some(widget)
+}
+
+fn apply_style(widget: *mut gtk::GtkWidget, style: &model::ElementStyle) {
+    unsafe {
+        gtk::gtk_widget_set_halign(widget, alignment(&style.horizontal_alignment));
+        if style.horizontal_alignment == Alignment::Fill {
+            gtk::gtk_widget_set_hexpand(widget, true.into());
+        }
+        gtk::gtk_widget_set_valign(widget, alignment(&style.vertical_alignment));
+        if style.vertical_alignment == Alignment::Fill {
+            gtk::gtk_widget_set_vexpand(widget, true.into());
+        }
+        gtk::gtk_widget_set_size_request(
+            widget,
+            style
+                .horizontal_size_request
+                .map(|v| v as i32)
+                .unwrap_or(-1),
+            style.vertical_size_request.map(|v| v as i32).unwrap_or(-1),
+        );
+
+        gtk::gtk_widget_set_margin_start(widget, style.margin.start as i32);
+        gtk::gtk_widget_set_margin_end(widget, style.margin.end as i32);
+        gtk::gtk_widget_set_margin_top(widget, style.margin.top as i32);
+        gtk::gtk_widget_set_margin_bottom(widget, style.margin.bottom as i32);
+    }
+    property_read_only! {
+        property &style.visible;
+        fn set(new_value: &bool) {
+            unsafe {
+                gtk::gtk_widget_set_visible(widget, new_value.clone().into());
+            };
+        }
+    }
+    property_read_only! {
+        property &style.enabled;
+        fn set(new_value: &bool) {
+            unsafe {
+                gtk::gtk_widget_set_sensitive(widget, new_value.clone().into());
+            }
+        }
+    }
+}
+
+fn alignment(align: &Alignment) -> gtk::GtkAlign {
+    use Alignment::*;
+    match align {
+        Start => gtk::GtkAlign_GTK_ALIGN_START,
+        Center => gtk::GtkAlign_GTK_ALIGN_CENTER,
+        End => gtk::GtkAlign_GTK_ALIGN_END,
+        Fill => gtk::GtkAlign_GTK_ALIGN_FILL,
+    }
+}
+
+struct PangoAttrList {
+    list: *mut gtk::PangoAttrList,
+}
+
+impl PangoAttrList {
+    pub fn new() -> Self {
+        PangoAttrList {
+            list: unsafe { gtk::pango_attr_list_new() },
+        }
+    }
+
+    pub fn bold(&mut self) -> &mut Self {
+        unsafe {
+            gtk::pango_attr_list_insert(
+                self.list,
+                gtk::pango_attr_weight_new(gtk::PangoWeight_PANGO_WEIGHT_BOLD),
+            )
+        };
+        self
+    }
+}
+
+impl std::ops::Deref for PangoAttrList {
+    type Target = *mut gtk::PangoAttrList;
+
+    fn deref(&self) -> &Self::Target {
+        &self.list
+    }
+}
+
+impl std::ops::DerefMut for PangoAttrList {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.list
+    }
+}
+
+impl Drop for PangoAttrList {
+    fn drop(&mut self) {
+        unsafe { gtk::pango_attr_list_unref(self.list) };
+    }
+}
+
+fn render_element_type(element_type: &model::ElementType) -> Option<*mut gtk::GtkWidget> {
+    use model::ElementType::*;
+    Some(match element_type {
+        Label(model::Label { text, bold }) => {
+            let label_ptr = unsafe { gtk::gtk_label_new(std::ptr::null()) };
+            match text {
+                Property::Static(text) => {
+                    let text = CString::new(text.clone()).ok()?;
+                    unsafe { gtk::gtk_label_set_text(label_ptr as _, text.as_ptr()) };
+                    text.drop_with_widget(label_ptr);
+                }
+                Property::Binding(b) => {
+                    let label_text = Rc::new(RefCell::new(CString::new(b.borrow().clone()).ok()?));
+                    unsafe {
+                        gtk::gtk_label_set_text(label_ptr as _, label_text.borrow().as_ptr())
+                    };
+                    let lt = label_text.clone();
+                    label_text.drop_with_widget(label_ptr);
+                    b.on_change(move |t| {
+                        let Some(cstr) = CString::new(t.clone()).ok() else {
+                            return;
+                        };
+                        unsafe { gtk::gtk_label_set_text(label_ptr as _, cstr.as_ptr()) };
+                        *lt.borrow_mut() = cstr;
+                    });
+                }
+                Property::ReadOnly(_) => unimplemented!("ReadOnly not supported for Label::text"),
+            }
+            unsafe { gtk::gtk_label_set_line_wrap(label_ptr as _, true.into()) };
+            // This is gtk_label_set_{xalign,yalign} in gtk 3.16+
+            unsafe { gtk::gtk_misc_set_alignment(label_ptr as _, 0.0, 0.5) };
+            if *bold {
+                unsafe {
+                    gtk::gtk_label_set_attributes(label_ptr as _, **PangoAttrList::new().bold())
+                };
+            }
+            label_ptr
+        }
+        HBox(model::HBox {
+            items,
+            spacing,
+            affirmative_order,
+        }) => {
+            let box_ptr =
+                unsafe { gtk::gtk_box_new(gtk::GtkOrientation_GTK_ORIENTATION_HORIZONTAL, 0) };
+            unsafe { gtk::gtk_box_set_spacing(box_ptr as *mut _, *spacing as i32) };
+            let items_iter: Box<dyn Iterator<Item = &Element>> = if *affirmative_order {
+                Box::new(items.iter().rev())
+            } else {
+                Box::new(items.iter())
+            };
+            for item in items_iter {
+                if let Some(widget) = render(item) {
+                    unsafe {
+                        gtk::gtk_container_add(box_ptr as *mut gtk::GtkContainer, widget);
+                    }
+                    // Special case horizontal alignment to pack into the end if appropriate
+                    if item.style.horizontal_alignment == Alignment::End {
+                        unsafe {
+                            gtk::gtk_box_set_child_packing(
+                                box_ptr as _,
+                                widget,
+                                false.into(),
+                                false.into(),
+                                0,
+                                gtk::GtkPackType_GTK_PACK_END,
+                            );
+                        }
+                    }
+                }
+            }
+            box_ptr
+        }
+        VBox(model::VBox { items, spacing }) => {
+            let box_ptr =
+                unsafe { gtk::gtk_box_new(gtk::GtkOrientation_GTK_ORIENTATION_VERTICAL, 0) };
+            unsafe { gtk::gtk_box_set_spacing(box_ptr as *mut _, *spacing as i32) };
+            for item in items {
+                if let Some(widget) = render(item) {
+                    unsafe {
+                        gtk::gtk_container_add(box_ptr as *mut gtk::GtkContainer, widget);
+                    }
+                    // Special case vertical alignment to pack into the end if appropriate
+                    if item.style.vertical_alignment == Alignment::End {
+                        unsafe {
+                            gtk::gtk_box_set_child_packing(
+                                box_ptr as _,
+                                widget,
+                                false.into(),
+                                false.into(),
+                                0,
+                                gtk::GtkPackType_GTK_PACK_END,
+                            );
+                        }
+                    }
+                }
+            }
+            box_ptr
+        }
+        Button(model::Button { content, click }) => {
+            let button_ptr = unsafe { gtk::gtk_button_new() };
+            if let Some(widget) = content.as_deref().and_then(render) {
+                unsafe {
+                    // Always center widgets in buttons.
+                    gtk::gtk_widget_set_valign(widget, alignment(&Alignment::Center));
+                    gtk::gtk_widget_set_halign(widget, alignment(&Alignment::Center));
+                    gtk::gtk_container_add(button_ptr as *mut gtk::GtkContainer, widget);
+                }
+            }
+            connect_signal! {
+                object button_ptr;
+                with click;
+                signal clicked(event: &Event<()>, _button: *mut gtk::GtkButton) {
+                    event.fire(&());
+                }
+            }
+            button_ptr
+        }
+        Checkbox(model::Checkbox { checked, label }) => {
+            let cb_ptr = match label {
+                None => unsafe { gtk::gtk_check_button_new() },
+                Some(s) => {
+                    let label = CString::new(s.clone()).ok()?;
+                    let cb = unsafe { gtk::gtk_check_button_new_with_label(label.as_ptr()) };
+                    label.drop_with_widget(cb);
+                    cb
+                }
+            };
+            property_with_signal! {
+                object cb_ptr;
+                property checked;
+                signal toggled;
+                fn set(new_value: &bool) {
+                    unsafe {
+                        gtk::gtk_toggle_button_set_active(cb_ptr as *mut _, new_value.clone().into())
+                    };
+                }
+                fn get(button: *mut gtk::GtkToggleButton) -> bool {
+                    unsafe {
+                        gtk::gtk_toggle_button_get_active(button) == 1
+                    }
+                }
+            }
+            cb_ptr
+        }
+        TextBox(model::TextBox {
+            placeholder,
+            content,
+            editable,
+        }) => {
+            let text_ptr = unsafe { gtk::gtk_text_view_new() };
+            unsafe {
+                const GTK_WRAP_WORD_CHAR: u32 = 3;
+                gtk::gtk_text_view_set_wrap_mode(text_ptr as *mut _, GTK_WRAP_WORD_CHAR);
+                gtk::gtk_text_view_set_editable(text_ptr as *mut _, editable.clone().into());
+                gtk::gtk_text_view_set_accepts_tab(text_ptr as *mut _, false.into());
+            }
+            let buffer = unsafe { gtk::gtk_text_view_get_buffer(text_ptr as *mut _) };
+
+            struct State {
+                placeholder: Option<Placeholder>,
+            }
+
+            struct Placeholder {
+                string: CString,
+                visible: RefCell<bool>,
+            }
+
+            impl Placeholder {
+                fn focus(&self, widget: *mut gtk::GtkWidget) {
+                    if *self.visible.borrow() {
+                        unsafe {
+                            let buffer = gtk::gtk_text_view_get_buffer(widget as *mut _);
+                            gtk::gtk_text_buffer_set_text(buffer, self.string.as_ptr(), 0);
+                            gtk::gtk_widget_override_color(
+                                widget,
+                                gtk::GtkStateFlags_GTK_STATE_FLAG_NORMAL,
+                                std::ptr::null(),
+                            );
+                        }
+                        *self.visible.borrow_mut() = false;
+                    }
+                }
+
+                fn unfocus(&self, widget: *mut gtk::GtkWidget) {
+                    unsafe {
+                        let buffer = gtk::gtk_text_view_get_buffer(widget as *mut _);
+
+                        let mut end_iter = gtk::GtkTextIter::default();
+                        gtk::gtk_text_buffer_get_end_iter(buffer, &mut end_iter);
+                        let is_empty = gtk::gtk_text_iter_get_offset(&end_iter) == 0;
+
+                        if is_empty && !*self.visible.borrow() {
+                            gtk::gtk_text_buffer_set_text(buffer, self.string.as_ptr(), -1);
+                            let context = gtk::gtk_widget_get_style_context(widget);
+                            let mut color = gtk::GdkRGBA::default();
+                            gtk::gtk_style_context_get_color(
+                                context,
+                                gtk::GtkStateFlags_GTK_STATE_FLAG_INSENSITIVE,
+                                &mut color,
+                            );
+                            gtk::gtk_widget_override_color(
+                                widget,
+                                gtk::GtkStateFlags_GTK_STATE_FLAG_NORMAL,
+                                &color,
+                            );
+                            *self.visible.borrow_mut() = true;
+                        }
+                    }
+                }
+            }
+
+            let mut state = Box::new(State { placeholder: None });
+
+            if let Some(placeholder) = placeholder {
+                state.placeholder = Some(Placeholder {
+                    string: CString::new(placeholder.clone()).ok()?,
+                    visible: RefCell::new(false),
+                });
+
+                let placeholder = state.placeholder.as_ref().unwrap();
+
+                placeholder.unfocus(text_ptr);
+
+                connect_signal! {
+                    object text_ptr;
+                    with placeholder;
+                    signal focus_in_event(placeholder: &Placeholder, widget: *mut gtk::GtkWidget,
+                                          _event: *mut gtk::GdkEventFocus) -> gtk::gboolean {
+                        placeholder.focus(widget);
+                        false.into()
+                    }
+                }
+                connect_signal! {
+                    object text_ptr;
+                    with placeholder;
+                    signal focus_out_event(placeholder: &Placeholder, widget: *mut gtk::GtkWidget,
+                                          _event: *mut gtk::GdkEventFocus) -> gtk::gboolean {
+                        placeholder.unfocus(widget);
+                        false.into()
+                    }
+                }
+            }
+
+            // Attach the state so that we can access it in the changed signal.
+            // This is kind of ugly; in the future it might be a nicer developer interface to simply
+            // always use a closure as the user data (which itself can capture arbitrary things). This
+            // would move the data management from GTK to rust.
+            state.set_data(buffer as *mut _, cstr!("textview-state"));
+
+            property_with_signal! {
+                object buffer;
+                property content;
+                signal changed;
+                fn set(new_value: &String) {
+                    unsafe {
+                        gtk::gtk_text_buffer_set_text(buffer, new_value.as_ptr() as *const c_char, new_value.len().try_into().unwrap());
+                    }
+                }
+                fn get(buffer: *mut gtk::GtkTextBuffer) -> String {
+                    let state = unsafe {
+                        gtk::g_object_get_data(buffer as *mut _, cstr!("textview-state"))
+                    };
+                    if !state.is_null() {
+                        let s: &State = unsafe { &*(state as *mut State as *const State) };
+                        if let Some(placeholder) = &s.placeholder {
+                            if *placeholder.visible.borrow() {
+                                return "".to_owned();
+                            }
+                        }
+                    }
+                    let mut start_iter = gtk::GtkTextIter::default();
+                    unsafe {
+                        gtk::gtk_text_buffer_get_start_iter(buffer, &mut start_iter);
+                    }
+
+                    let mut s = String::new();
+                    loop {
+                        let c = unsafe { gtk::gtk_text_iter_get_char(&start_iter) };
+                        if c == 0 {
+                            break;
+                        }
+                        // Safety:
+                        // gunichar is guaranteed to be a valid unicode codepoint (if nonzero).
+                        s.push(unsafe { char::from_u32_unchecked(c) });
+                        unsafe {
+                            gtk::gtk_text_iter_forward_char(&mut start_iter);
+                        }
+                    }
+                    s
+                }
+            }
+            text_ptr
+        }
+        Scroll(model::Scroll { content }) => {
+            let scroll_ptr =
+                unsafe { gtk::gtk_scrolled_window_new(std::ptr::null_mut(), std::ptr::null_mut()) };
+            unsafe {
+                gtk::gtk_scrolled_window_set_policy(
+                    scroll_ptr as *mut _,
+                    gtk::GtkPolicyType_GTK_POLICY_NEVER,
+                    gtk::GtkPolicyType_GTK_POLICY_ALWAYS,
+                );
+                gtk::gtk_scrolled_window_set_shadow_type(
+                    scroll_ptr as *mut _,
+                    gtk::GtkShadowType_GTK_SHADOW_IN,
+                );
+            };
+            if let Some(widget) = content.as_deref().and_then(render) {
+                unsafe {
+                    gtk::gtk_container_add(scroll_ptr as *mut gtk::GtkContainer, widget);
+                }
+            }
+            scroll_ptr
+        }
+        Progress(model::Progress { amount }) => {
+            let progress_ptr = unsafe { gtk::gtk_progress_bar_new() };
+            property_read_only! {
+                property amount;
+                fn set(value: &Option<f32>) {
+                    match &*value {
+                        Some(v) => unsafe {
+                            gtk::gtk_progress_bar_set_fraction(
+                                progress_ptr as *mut _,
+                                v.clamp(0f32,1f32) as f64,
+                            );
+                        }
+                        None => unsafe {
+                            gtk::gtk_progress_bar_pulse(progress_ptr as *mut _);
+
+                            fn auto_pulse_progress_bar(progress: *mut gtk::GtkProgressBar) {
+                                unsafe extern fn pulse(progress: *mut std::ffi::c_void) -> gtk::gboolean {
+                                    if gtk::gtk_widget_is_visible(progress as _) == 0 {
+                                        false.into()
+                                    } else {
+                                        gtk::gtk_progress_bar_pulse(progress as _);
+                                        true.into()
+                                    }
+                                }
+                                unsafe {
+                                    gtk::g_timeout_add(100, Some(pulse as unsafe extern fn(*mut std::ffi::c_void) -> gtk::gboolean), progress as _);
+                                }
+
+                            }
+
+                            connect_signal! {
+                                object progress_ptr;
+                                with std::ptr::null_mut();
+                                signal show(_user_data: &(), progress: *mut gtk::GtkWidget) {
+                                    auto_pulse_progress_bar(progress as *mut _);
+                                }
+                            }
+                            auto_pulse_progress_bar(progress_ptr as *mut _);
+                        }
+                    }
+                }
+            }
+            progress_ptr
+        }
+    })
+}
+
+fn render_window(
+    model::Window {
+        title,
+        content,
+        children,
+        modal,
+        close,
+    }: &model::Window,
+) -> *mut gtk::GtkWidget {
+    unsafe {
+        let window_ptr = gtk::gtk_window_new(gtk::GtkWindowType_GTK_WINDOW_TOPLEVEL);
+        if !title.is_empty() {
+            if let Some(title) = CString::new(title.clone()).ok() {
+                gtk::gtk_window_set_title(window_ptr as *mut _, title.as_ptr());
+                title.drop_with_widget(window_ptr);
+            }
+        }
+        if let Some(content) = content {
+            if let Some(widget) = render(content) {
+                gtk::gtk_container_add(window_ptr as *mut gtk::GtkContainer, widget);
+            }
+        }
+        for child in children {
+            let widget = render_window(&child.element_type);
+            apply_style(widget, &child.style);
+            gtk::gtk_window_set_transient_for(widget as *mut _, window_ptr as *mut _);
+            // Delete should hide the window.
+            gtk::g_signal_connect_data(
+                widget as *mut _,
+                cstr!("delete-event"),
+                Some(std::mem::transmute(
+                    gtk::gtk_widget_hide_on_delete
+                        as unsafe extern "C" fn(*mut gtk::GtkWidget) -> i32,
+                )),
+                std::ptr::null_mut(),
+                None,
+                0,
+            );
+        }
+        if *modal {
+            gtk::gtk_window_set_modal(window_ptr as *mut _, true.into());
+        }
+        if let Some(close) = close {
+            close.subscribe(move |&()| gtk::gtk_window_close(window_ptr as *mut _));
+        }
+
+        window_ptr
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/ui/macos/mod.rs b/toolkit/crashreporter/client/app/src/ui/macos/mod.rs
new file mode 100644
index 0000000000..6520d16472
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/ui/macos/mod.rs
@@ -0,0 +1,1122 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! A UI using the macos cocoa API.
+//!
+//! This UI contains some edge cases that aren't implemented, for instance:
+//! * there are a few cases where specific hierarchies are handled differently (e.g. a Button
+//!   containing Label), etc.
+//! * not all controls handle all Property variants (e.g. Checkbox doesn't handle ReadOnly, Text
+//!   doesn't handle Binding, etc).
+//!
+//! The rendering ignores `ElementStyle::margin` entirely, because
+//! * `NSView` doesn't support margins (so working them into constraints would be a bit annoying),
+//!   and
+//! * `NSView.layoutMarginsGuide` results in a layout almost identical to what the margins (at the
+//!   time of this writing) in the UI layouts are achieving.
+//!
+//! In a few cases, init or creation functions are called which _could_ return nil and are wrapped
+//! in their type wrapper (as those functions return `instancetype`/`id`). We consider this safe
+//! enough because it won't cause unsoundness (they are only passed to objc functions which can
+//! take nil arguments) and the failure case is very unlikely.
+
+#![allow(non_upper_case_globals)]
+
+use self::objc::*;
+use super::model::{self, Alignment, Application, Element, TypedElement};
+use crate::data::Property;
+use cocoa::{
+    INSApplication, INSBox, INSButton, INSColor, INSControl, INSFont, INSLayoutAnchor,
+    INSLayoutConstraint, INSLayoutDimension, INSLayoutGuide, INSMenu, INSMenuItem,
+    INSMutableParagraphStyle, INSObject, INSProcessInfo, INSProgressIndicator, INSRunLoop,
+    INSScrollView, INSStackView, INSText, INSTextContainer, INSTextField, INSTextView, INSView,
+    INSWindow, NSArray_NSArrayCreation, NSAttributedString_NSExtendedAttributedString,
+    NSDictionary_NSDictionaryCreation, NSRunLoop_NSRunLoopConveniences,
+    NSStackView_NSStackViewGravityAreas, NSString_NSStringExtensionMethods,
+    NSTextField_NSTextFieldConvenience, NSView_NSConstraintBasedLayoutInstallingConstraints,
+    NSView_NSConstraintBasedLayoutLayering, NSView_NSSafeAreas, PNSObject,
+};
+use once_cell::sync::Lazy;
+
+/// https://developer.apple.com/documentation/foundation/1497293-string_encodings/nsutf8stringencoding?language=objc
+const NSUTF8StringEncoding: cocoa::NSStringEncoding = 4;
+
+/// Constant from NSCell.h
+const NSControlStateValueOn: cocoa::NSControlStateValue = 1;
+
+/// Constant from NSLayoutConstraint.h
+const NSLayoutPriorityDefaultHigh: cocoa::NSLayoutPriority = 750.0;
+
+mod objc;
+
+/// A MacOS Cocoa UI implementation.
+#[derive(Default)]
+pub struct UI;
+
+impl UI {
+    pub fn run_loop(&self, app: Application) {
+        let nsapp = unsafe { cocoa::NSApplication::sharedApplication() };
+
+        Objc::<AppDelegate>::register();
+        Objc::<Button>::register();
+        Objc::<Checkbox>::register();
+        Objc::<TextView>::register();
+        Objc::<Window>::register();
+
+        rc::autoreleasepool(|| {
+            let delegate = AppDelegate::new(app).into_object();
+            // Set delegate
+            unsafe { nsapp.setDelegate_(delegate.instance as *mut _) };
+
+            // Set up the main menu
+            unsafe {
+                let appname = read_nsstring(cocoa::NSProcessInfo::processInfo().processName());
+                let mainmenu = StrongRef::new(cocoa::NSMenu::alloc());
+                mainmenu.init();
+
+                {
+                    // We don't need a title for the app menu item nor menu; it will always come from
+                    // the process name regardless of what we set.
+                    let appmenuitem = StrongRef::new(cocoa::NSMenuItem::alloc()).autorelease();
+                    appmenuitem.init();
+                    mainmenu.addItem_(appmenuitem);
+
+                    let appmenu = StrongRef::new(cocoa::NSMenu::alloc());
+                    appmenu.init();
+
+                    {
+                        let quit = StrongRef::new(cocoa::NSMenuItem::alloc());
+                        quit.initWithTitle_action_keyEquivalent_(
+                            nsstring(&format!("Quit {appname}")),
+                            sel!(terminate:),
+                            nsstring("q"),
+                        );
+                        appmenu.addItem_(quit.autorelease());
+                    }
+                    appmenuitem.setSubmenu_(appmenu.autorelease());
+                }
+                {
+                    let editmenuitem = StrongRef::new(cocoa::NSMenuItem::alloc()).autorelease();
+                    editmenuitem.initWithTitle_action_keyEquivalent_(
+                        nsstring("Edit"),
+                        runtime::Sel::from_ptr(std::ptr::null()),
+                        nsstring(""),
+                    );
+                    mainmenu.addItem_(editmenuitem);
+
+                    let editmenu = StrongRef::new(cocoa::NSMenu::alloc());
+                    editmenu.initWithTitle_(nsstring("Edit"));
+
+                    let add_item = |name, selector, shortcut| {
+                        let item = StrongRef::new(cocoa::NSMenuItem::alloc());
+                        item.initWithTitle_action_keyEquivalent_(
+                            nsstring(name),
+                            selector,
+                            nsstring(shortcut),
+                        );
+                        editmenu.addItem_(item.autorelease());
+                    };
+
+                    add_item("Undo", sel!(undo:), "z");
+                    add_item("Redo", sel!(redo:), "Z");
+                    editmenu.addItem_(cocoa::NSMenuItem::separatorItem());
+                    add_item("Cut", sel!(cut:), "x");
+                    add_item("Copy", sel!(copy:), "c");
+                    add_item("Paste", sel!(paste:), "v");
+                    add_item("Delete", sel!(delete:), "");
+                    add_item("Select All", sel!(selectAll:), "a");
+
+                    editmenuitem.setSubmenu_(editmenu.autorelease());
+                }
+
+                nsapp.setMainMenu_(mainmenu.autorelease());
+            }
+
+            // Run the main application loop
+            unsafe { nsapp.run() };
+        });
+    }
+
+    pub fn invoke(&self, f: model::InvokeFn) {
+        // Blocks only take `Fn`, so we have to wrap the boxed function.
+        let f = std::cell::RefCell::new(Some(f));
+        enqueue(move || {
+            if let Some(f) = f.borrow_mut().take() {
+                f();
+            }
+        });
+    }
+}
+
+fn enqueue<F: Fn() + 'static>(f: F) {
+    let block = block::ConcreteBlock::new(f);
+    // The block must be an RcBlock so addOperationWithBlock can retain it.
+    // https://docs.rs/block/latest/block/#creating-blocks
+    let block = block.copy();
+
+    // We need to explicitly signal that the enqueued blocks can run in both the default mode (the
+    // main loop) and modal mode, otherwise when modal windows are opened things get stuck.
+    struct RunloopModes(cocoa::NSArray);
+
+    impl RunloopModes {
+        pub fn new() -> Self {
+            unsafe {
+                let objects: [cocoa::id; 2] = [
+                    cocoa::NSDefaultRunLoopMode.0,
+                    cocoa::NSModalPanelRunLoopMode.0,
+                ];
+                RunloopModes(
+                    cocoa::NSArray(<cocoa::NSArray as NSArray_NSArrayCreation<
+                        cocoa::NSRunLoopMode,
+                    >>::arrayWithObjects_count_(
+                        objects.as_slice().as_ptr() as *const *mut u64,
+                        objects
+                            .as_slice()
+                            .len()
+                            .try_into()
+                            .expect("usize can't fit in u64"),
+                    )),
+                )
+            }
+        }
+    }
+
+    // # Safety
+    // The array is static and cannot be changed.
+    unsafe impl Sync for RunloopModes {}
+    unsafe impl Send for RunloopModes {}
+
+    static RUNLOOP_MODES: Lazy<RunloopModes> = Lazy::new(RunloopModes::new);
+
+    unsafe {
+        cocoa::NSRunLoop::mainRunLoop().performInModes_block_(RUNLOOP_MODES.0, &*block);
+    }
+}
+
+#[repr(transparent)]
+struct Rect(pub cocoa::NSRect);
+
+unsafe impl Encode for Rect {
+    fn encode() -> Encoding {
+        unsafe { Encoding::from_str("{CGRect={CGPoint=dd}{CGSize=dd}}") }
+    }
+}
+
+/// Create an NSString by copying a str.
+fn nsstring(v: &str) -> cocoa::NSString {
+    unsafe {
+        StrongRef::new(cocoa::NSString(
+            cocoa::NSString::alloc().initWithBytes_length_encoding_(
+                v.as_ptr() as *const _,
+                v.len().try_into().expect("usize can't fit in u64"),
+                NSUTF8StringEncoding,
+            ),
+        ))
+    }
+    .autorelease()
+}
+
+/// Create a String by copying an NSString
+fn read_nsstring(s: cocoa::NSString) -> String {
+    let c_str = unsafe { std::ffi::CStr::from_ptr(s.UTF8String()) };
+    c_str.to_str().expect("NSString isn't UTF8").to_owned()
+}
+
+fn nsrect<X: Into<f64>, Y: Into<f64>, W: Into<f64>, H: Into<f64>>(
+    x: X,
+    y: Y,
+    w: W,
+    h: H,
+) -> cocoa::NSRect {
+    cocoa::NSRect {
+        origin: cocoa::NSPoint {
+            x: x.into(),
+            y: y.into(),
+        },
+        size: cocoa::NSSize {
+            width: w.into(),
+            height: h.into(),
+        },
+    }
+}
+
+struct AppDelegate {
+    app: Option<Application>,
+    windows: Vec<StrongRef<cocoa::NSWindow>>,
+}
+
+impl AppDelegate {
+    pub fn new(app: Application) -> Self {
+        AppDelegate {
+            app: Some(app),
+            windows: Default::default(),
+        }
+    }
+}
+
+objc_class! {
+    impl AppDelegate: NSObject /*<NSApplicationDelegate>*/ {
+        #[sel(applicationDidFinishLaunching:)]
+        fn application_did_finish_launching(&mut self, _notification: Ptr<cocoa::NSNotification>) {
+            // Activate the application (bringing windows to the active foreground later)
+            unsafe { cocoa::NSApplication::sharedApplication().activateIgnoringOtherApps_(runtime::YES) };
+
+            let mut first = true;
+            let mut windows = WindowRenderer::default();
+            let app = self.app.take().unwrap();
+            windows.rtl = app.rtl;
+            for window in app.windows {
+                let w = windows.render(window);
+                unsafe {
+                    if first {
+                        w.makeKeyAndOrderFront_(self.instance);
+                        w.makeMainWindow();
+                        first = false;
+                    }
+                }
+            }
+            self.windows = windows.unwrap();
+
+        }
+
+        #[sel(applicationShouldTerminateAfterLastWindowClosed:)]
+        fn application_should_terminate_after_window_closed(&mut self, _app: Ptr<cocoa::NSApplication>) -> runtime::BOOL {
+            runtime::YES
+        }
+    }
+}
+
+struct Window {
+    modal: bool,
+    title: String,
+    style: model::ElementStyle,
+}
+
+objc_class! {
+    impl Window: NSWindow /*<NSWindowDelegate>*/ {
+        #[sel(init)]
+        fn init(&mut self) -> cocoa::id {
+            let style = &self.style;
+            let title = &self.title;
+            let w = cocoa::NSWindow(self.instance);
+
+            unsafe {
+                if w.initWithContentRect_styleMask_backing_defer_(
+                    nsrect(
+                        0,
+                        0,
+                        style.horizontal_size_request.unwrap_or(800),
+                        style.vertical_size_request.unwrap_or(500),
+                    ),
+                    cocoa::NSWindowStyleMaskTitled
+                        | cocoa::NSWindowStyleMaskClosable
+                        | cocoa::NSWindowStyleMaskResizable
+                        | cocoa::NSWindowStyleMaskMiniaturizable,
+                    cocoa::NSBackingStoreBuffered,
+                    runtime::NO,
+                ).is_null() {
+                    return std::ptr::null_mut();
+                }
+
+                w.setDelegate_(self.instance as _);
+                w.setMinSize_(cocoa::NSSize {
+                    width: style.horizontal_size_request.unwrap_or(0) as f64,
+                    height: style.vertical_size_request.unwrap_or(0) as f64,
+                });
+
+                if !title.is_empty() {
+                    w.setTitle_(nsstring(title.as_str()));
+                }
+            }
+
+            self.instance
+        }
+
+        #[sel(windowWillClose:)]
+        fn window_will_close(&mut self, _notification: Ptr<cocoa::NSNotification>) {
+            if self.modal {
+                unsafe {
+                    let nsapp = cocoa::NSApplication::sharedApplication();
+                    nsapp.stopModal();
+                }
+            }
+        }
+    }
+}
+
+impl From<Objc<Window>> for cocoa::NSWindow {
+    fn from(ptr: Objc<Window>) -> Self {
+        cocoa::NSWindow(ptr.instance)
+    }
+}
+
+struct Button {
+    element: model::Button,
+}
+
+impl Button {
+    pub fn with_title(self, title: &str) -> cocoa::NSButton {
+        let obj = self.into_object();
+        unsafe {
+            let () = msg_send![obj.instance, setTitle: nsstring(title)];
+        }
+        // # Safety
+        // NSButton is the superclass of Objc<Button>.
+        unsafe { std::mem::transmute(obj.autorelease()) }
+    }
+}
+
+objc_class! {
+    impl Button: NSButton {
+        #[sel(initWithFrame:)]
+        fn init_with_frame(&mut self, frame_rect: Rect) -> cocoa::id {
+            unsafe {
+                let object: cocoa::id = msg_send![super(self.instance, class!(NSButton)), initWithFrame: frame_rect.0];
+                if object.is_null() {
+                    return object;
+                }
+                let () = msg_send![object, setBezelStyle: cocoa::NSBezelStyleRounded];
+                let () = msg_send![object, setAction: sel!(didClick)];
+                let () = msg_send![object, setTarget: object];
+                object
+            }
+        }
+
+        #[sel(didClick)]
+        fn did_click(&mut self) {
+            self.element.click.fire(&());
+        }
+    }
+}
+
+struct Checkbox {
+    element: model::Checkbox,
+}
+
+objc_class! {
+    impl Checkbox: NSButton {
+        #[sel(initWithFrame:)]
+        fn init_with_frame(&mut self, frame_rect: Rect) -> cocoa::id {
+            unsafe {
+                let object: cocoa::id = msg_send![super(self.instance, class!(NSButton)), initWithFrame: frame_rect.0];
+                if object.is_null() {
+                    return object;
+                }
+                let () = msg_send![object, setButtonType: cocoa::NSButtonTypeSwitch];
+                if let Some(label) = &self.element.label {
+                    let () = msg_send![object, setTitle: nsstring(label.as_str())];
+                }
+                let () = msg_send![object, setAction: sel!(didClick:)];
+                let () = msg_send![object, setTarget: object];
+
+                match &self.element.checked {
+                    Property::Binding(s) => {
+                        if *s.borrow() {
+                            let () = msg_send![object, setState: NSControlStateValueOn];
+                        }
+                    }
+                    Property::ReadOnly(_) => (),
+                    Property::Static(_) => (),
+                }
+
+                object
+            }
+        }
+
+        #[sel(didClick:)]
+        fn did_click(&mut self, button: Objc<Checkbox>) {
+            match &self.element.checked {
+                Property::Binding(s) => {
+                    let state = unsafe { std::mem::transmute::<_, cocoa::NSButton>(button).state() };
+                    *s.borrow_mut() = state == NSControlStateValueOn;
+                }
+                Property::ReadOnly(_) => (),
+                Property::Static(_) => (),
+            }
+        }
+    }
+}
+
+impl Checkbox {
+    pub fn into_button(self) -> cocoa::NSButton {
+        let obj = self.into_object();
+        // # Safety
+        // NSButton is the superclass of Objc<Checkbox>.
+        unsafe { std::mem::transmute(obj.autorelease()) }
+    }
+}
+
+struct TextView;
+
+objc_class! {
+    impl TextView: NSTextView /*<NSTextViewDelegate>*/ {
+        #[sel(initWithFrame:)]
+        fn init_with_frame(&mut self, frame_rect: Rect) -> cocoa::id {
+            unsafe {
+                let object: cocoa::id = msg_send![super(self.instance, class!(NSTextView)), initWithFrame: frame_rect.0];
+                if object.is_null() {
+                    return object;
+                }
+                let () = msg_send![object, setDelegate: self.instance];
+                object
+            }
+        }
+
+        #[sel(textView:doCommandBySelector:)]
+        fn do_command_by_selector(&mut self, text_view: Ptr<cocoa::NSTextView>, selector: runtime::Sel) -> runtime::BOOL {
+            let Ptr(text_view) = text_view;
+            // Make Tab/Backtab navigate to key views rather than inserting tabs in the text view.
+            // We can't use the `NSText` `fieldEditor` property to implement this behavior because
+            // that will disable the Enter key.
+            if selector == sel!(insertTab:) {
+                unsafe { text_view.window().selectNextKeyView_(text_view.0) };
+                return runtime::YES;
+            } else if selector == sel!(insertBacktab:) {
+                unsafe { text_view.window().selectPreviousKeyView_(text_view.0) };
+                return runtime::YES;
+            }
+            runtime::NO
+        }
+    }
+}
+
+impl From<Objc<TextView>> for cocoa::NSTextView {
+    fn from(tv: Objc<TextView>) -> Self {
+        // # Safety
+        // NSTextView is the superclass of Objc<TextView>.
+        unsafe { std::mem::transmute(tv) }
+    }
+}
+
+// For some reason the bindgen code for the nslayoutanchor subclasses doesn't have
+// `Into<NSLayoutAnchor>`, so we add our own.
+trait IntoNSLayoutAnchor {
+    fn into_layout_anchor(self) -> cocoa::NSLayoutAnchor;
+}
+
+impl IntoNSLayoutAnchor for cocoa::NSLayoutXAxisAnchor {
+    fn into_layout_anchor(self) -> cocoa::NSLayoutAnchor {
+        // # Safety
+        // NSLayoutXAxisAnchor is a subclass of NSLayoutAnchor
+        cocoa::NSLayoutAnchor(self.0)
+    }
+}
+
+impl IntoNSLayoutAnchor for cocoa::NSLayoutYAxisAnchor {
+    fn into_layout_anchor(self) -> cocoa::NSLayoutAnchor {
+        // # Safety
+        // NSLayoutYAxisAnchor is a subclass of NSLayoutAnchor
+        cocoa::NSLayoutAnchor(self.0)
+    }
+}
+
+unsafe fn constraint_equal<T, O>(anchor: T, to: O)
+where
+    T: INSLayoutAnchor<()> + std::ops::Deref,
+    T::Target: Message + Sized,
+    O: IntoNSLayoutAnchor,
+{
+    anchor
+        .constraintEqualToAnchor_(to.into_layout_anchor())
+        .setActive_(runtime::YES);
+}
+
+#[derive(Default)]
+struct WindowRenderer {
+    windows_to_retain: Vec<StrongRef<cocoa::NSWindow>>,
+    rtl: bool,
+}
+
+impl WindowRenderer {
+    pub fn unwrap(self) -> Vec<StrongRef<cocoa::NSWindow>> {
+        self.windows_to_retain
+    }
+
+    pub fn render(&mut self, window: TypedElement<model::Window>) -> StrongRef<cocoa::NSWindow> {
+        let style = window.style;
+        let model::Window {
+            close,
+            children,
+            content,
+            modal,
+            title,
+        } = window.element_type;
+
+        let w = Window {
+            modal,
+            title,
+            style,
+        }
+        .into_object();
+
+        let nswindow: StrongRef<cocoa::NSWindow> = w.clone().cast();
+
+        unsafe {
+            // Don't release windows when closed: we retain windows at the top-level.
+            nswindow.setReleasedWhenClosed_(runtime::NO);
+
+            if let Some(close) = close {
+                let nswindow = nswindow.weak();
+                close.subscribe(move |&()| {
+                    if let Some(nswindow) = nswindow.lock() {
+                        nswindow.close();
+                    }
+                });
+            }
+
+            if let Some(e) = content {
+                // Use an NSBox as a container view so that the window's content can easily have
+                // constraints set up relative to the parent (they can't be set relative to the
+                // window).
+                let content_parent: StrongRef<cocoa::NSBox> = msg_send![class!(NSBox), new];
+                content_parent.setTitlePosition_(cocoa::NSNoTitle);
+                content_parent.setTransparent_(runtime::YES);
+                content_parent.setContentViewMargins_(cocoa::NSSize {
+                    width: 5.0,
+                    height: 5.0,
+                });
+                if ViewRenderer::new_with_selector(self.rtl, *content_parent, sel!(setContentView:))
+                    .render(*e)
+                {
+                    nswindow.setContentView_((*content_parent).into());
+                }
+            }
+
+            for child in children {
+                let modal = child.element_type.modal;
+                let visible = child.style.visible.clone();
+                let child_window = self.render(child);
+
+                #[derive(Clone, Copy)]
+                struct ShowChild {
+                    modal: bool,
+                }
+
+                impl ShowChild {
+                    pub fn show(&self, parent: cocoa::NSWindow, child: cocoa::NSWindow) {
+                        unsafe {
+                            parent.addChildWindow_ordered_(child, cocoa::NSWindowAbove);
+                            child.makeKeyAndOrderFront_(parent.0);
+                            if self.modal {
+                                // Run the modal from the main nsapp.run() loop to prevent binding
+                                // updates from being nested (as this will block until the modal is
+                                // stopped).
+                                enqueue(move || {
+                                    let nsapp = cocoa::NSApplication::sharedApplication();
+                                    nsapp.runModalForWindow_(child);
+                                });
+                            }
+                        }
+                    }
+                }
+
+                let show_child = ShowChild { modal };
+
+                match visible {
+                    Property::Static(visible) => {
+                        if visible {
+                            show_child.show(*nswindow, *child_window);
+                        }
+                    }
+                    Property::Binding(b) => {
+                        let child = child_window.weak();
+                        let parent = nswindow.weak();
+                        b.on_change(move |visible| {
+                            let Some((w, child_window)) = parent.lock().zip(child.lock()) else {
+                                return;
+                            };
+                            if *visible {
+                                show_child.show(*w, *child_window);
+                            } else {
+                                child_window.close();
+                            }
+                        });
+                        if *b.borrow() {
+                            show_child.show(*nswindow, *child_window);
+                        }
+                    }
+                    Property::ReadOnly(_) => panic!("window visibility cannot be ReadOnly"),
+                }
+            }
+        }
+        self.windows_to_retain.push(nswindow.clone());
+        nswindow
+    }
+}
+
+struct ViewRenderer {
+    parent: cocoa::NSView,
+    add_subview: Box<dyn Fn(cocoa::NSView, &model::ElementStyle, cocoa::NSView)>,
+    ignore_vertical: bool,
+    ignore_horizontal: bool,
+    rtl: bool,
+}
+
+impl ViewRenderer {
+    /// add_subview should add the rendered child view.
+    pub fn new<F>(rtl: bool, parent: impl Into<cocoa::NSView>, add_subview: F) -> Self
+    where
+        F: Fn(cocoa::NSView, &model::ElementStyle, cocoa::NSView) + 'static,
+    {
+        ViewRenderer {
+            parent: parent.into(),
+            add_subview: Box::new(add_subview),
+            ignore_vertical: false,
+            ignore_horizontal: false,
+            rtl,
+        }
+    }
+
+    /// add_subview should be the selector to call on the parent view to add the rendered child view.
+    pub fn new_with_selector(
+        rtl: bool,
+        parent: impl Into<cocoa::NSView>,
+        add_subview: runtime::Sel,
+    ) -> Self {
+        Self::new(rtl, parent, move |parent, _style, child| {
+            let () = unsafe { (*parent.0).send_message(add_subview, (child,)) }.unwrap();
+        })
+    }
+
+    /// Ignore vertical layout settings when rendering views.
+    pub fn ignore_vertical(mut self, setting: bool) -> Self {
+        self.ignore_vertical = setting;
+        self
+    }
+
+    /// Ignore horizontal layout settings when rendering views.
+    pub fn ignore_horizontal(mut self, setting: bool) -> Self {
+        self.ignore_horizontal = setting;
+        self
+    }
+
+    /// Render the given element.
+    ///
+    /// Returns whether the element was rendered.
+    pub fn render(
+        &self,
+        Element {
+            style,
+            element_type,
+        }: Element,
+    ) -> bool {
+        let Some(view) = render_element(element_type, &style, self.rtl) else {
+            return false;
+        };
+
+        (self.add_subview)(self.parent, &style, view);
+
+        // Setting the content hugging priority to a high value causes stackviews to not stretch
+        // subviews during autolayout.
+        unsafe {
+            view.setContentHuggingPriority_forOrientation_(
+                NSLayoutPriorityDefaultHigh,
+                cocoa::NSLayoutConstraintOrientationHorizontal,
+            );
+            view.setContentHuggingPriority_forOrientation_(
+                NSLayoutPriorityDefaultHigh,
+                cocoa::NSLayoutConstraintOrientationVertical,
+            );
+        }
+
+        // Set layout and writing direction based on RTL.
+        unsafe {
+            view.setUserInterfaceLayoutDirection_(if self.rtl {
+                cocoa::NSUserInterfaceLayoutDirectionRightToLeft
+            } else {
+                cocoa::NSUserInterfaceLayoutDirectionLeftToRight
+            });
+            if let Ok(control) = cocoa::NSControl::try_from(view) {
+                control.setBaseWritingDirection_(if self.rtl {
+                    cocoa::NSWritingDirectionRightToLeft
+                } else {
+                    cocoa::NSWritingDirectionLeftToRight
+                });
+            }
+        }
+
+        let lmg = unsafe { self.parent.layoutMarginsGuide() };
+
+        if !matches!(style.horizontal_alignment, Alignment::Fill) {
+            if let Some(size) = style.horizontal_size_request {
+                unsafe {
+                    view.widthAnchor()
+                        .constraintGreaterThanOrEqualToConstant_(size as _)
+                        .setActive_(runtime::YES);
+                }
+            }
+        }
+
+        if !self.ignore_horizontal {
+            unsafe {
+                let la = view.leadingAnchor();
+                let ta = view.trailingAnchor();
+                let pla = lmg.leadingAnchor();
+                let pta = lmg.trailingAnchor();
+                match style.horizontal_alignment {
+                    Alignment::Fill => {
+                        constraint_equal(la, pla);
+                        constraint_equal(ta, pta);
+                        // Without the autoresizing mask set, Text within Scroll doesn't display
+                        // properly (it shrinks to 0-width, likely due to some specific interaction
+                        // of NSScrollView with autolayout).
+                        view.setAutoresizingMask_(cocoa::NSViewWidthSizable);
+                    }
+                    Alignment::Start => {
+                        constraint_equal(la, pla);
+                    }
+                    Alignment::Center => {
+                        let ca = view.centerXAnchor();
+                        let pca = lmg.centerXAnchor();
+                        constraint_equal(ca, pca);
+                    }
+                    Alignment::End => {
+                        constraint_equal(ta, pta);
+                    }
+                }
+            }
+        }
+
+        if !matches!(style.vertical_alignment, Alignment::Fill) {
+            if let Some(size) = style.vertical_size_request {
+                unsafe {
+                    view.heightAnchor()
+                        .constraintGreaterThanOrEqualToConstant_(size as _)
+                        .setActive_(runtime::YES);
+                }
+            }
+        }
+
+        if !self.ignore_vertical {
+            unsafe {
+                let ta = view.topAnchor();
+                let ba = view.bottomAnchor();
+                let pta = lmg.topAnchor();
+                let pba = lmg.bottomAnchor();
+                match style.vertical_alignment {
+                    Alignment::Fill => {
+                        constraint_equal(ta, pta);
+                        constraint_equal(ba, pba);
+                        // Set the autoresizing mask to be consistent with the horizontal settings
+                        // (see the comment there as to why it's necessary).
+                        view.setAutoresizingMask_(cocoa::NSViewHeightSizable);
+                    }
+                    Alignment::Start => {
+                        constraint_equal(ta, pta);
+                    }
+                    Alignment::Center => {
+                        let ca = view.centerYAnchor();
+                        let pca = lmg.centerYAnchor();
+                        constraint_equal(ca, pca);
+                    }
+                    Alignment::End => {
+                        constraint_equal(ba, pba);
+                    }
+                }
+            }
+        }
+
+        match &style.visible {
+            Property::Static(ref v) => {
+                unsafe { view.setHidden_((!v).into()) };
+            }
+            Property::Binding(b) => {
+                b.on_change(move |&visible| unsafe {
+                    view.setHidden_((!visible).into());
+                });
+                unsafe { view.setHidden_((!*b.borrow()).into()) };
+            }
+            Property::ReadOnly(_) => {
+                unimplemented!("ElementStyle::visible doesn't support ReadOnly")
+            }
+        }
+
+        if let Ok(control) = cocoa::NSControl::try_from(view) {
+            match &style.enabled {
+                Property::Static(e) => {
+                    unsafe { control.setEnabled_((*e).into()) };
+                }
+                Property::Binding(b) => {
+                    b.on_change(move |&enabled| unsafe {
+                        control.setEnabled_(enabled.into());
+                    });
+                    unsafe { control.setEnabled_((*b.borrow()).into()) };
+                }
+                Property::ReadOnly(_) => {
+                    unimplemented!("ElementStyle::enabled doesn't support ReadOnly")
+                }
+            }
+        } else if let Ok(text) = cocoa::NSText::try_from(view) {
+            let normally_editable = unsafe { text.isEditable() } == runtime::YES;
+            let normally_selectable = unsafe { text.isSelectable() } == runtime::YES;
+            let set_enabled = move |enabled: bool| unsafe {
+                if !enabled {
+                    let mut range = text.selectedRange();
+                    range.length = 0;
+                    text.setSelectedRange_(range);
+                }
+                text.setEditable_((enabled && normally_editable).into());
+                text.setSelectable_((enabled && normally_selectable).into());
+                text.setBackgroundColor_(if enabled {
+                    cocoa::NSColor::textBackgroundColor()
+                } else {
+                    cocoa::NSColor::windowBackgroundColor()
+                });
+                text.setTextColor_(if enabled {
+                    cocoa::NSColor::textColor()
+                } else {
+                    cocoa::NSColor::disabledControlTextColor()
+                });
+            };
+            match &style.enabled {
+                Property::Static(e) => set_enabled(*e),
+                Property::Binding(b) => {
+                    b.on_change(move |&enabled| set_enabled(enabled));
+                    set_enabled(*b.borrow());
+                }
+                Property::ReadOnly(_) => {
+                    unimplemented!("ElementStyle::enabled doesn't support ReadOnly")
+                }
+            }
+        }
+
+        unsafe { view.setNeedsDisplay_(runtime::YES) };
+
+        true
+    }
+}
+
+fn render_element(
+    element_type: model::ElementType,
+    style: &model::ElementStyle,
+    rtl: bool,
+) -> Option<cocoa::NSView> {
+    use model::ElementType::*;
+    Some(match element_type {
+        VBox(model::VBox { items, spacing }) => {
+            let sv = unsafe { StrongRef::new(cocoa::NSStackView::alloc()) }.autorelease();
+            unsafe {
+                sv.init();
+                sv.setOrientation_(cocoa::NSUserInterfaceLayoutOrientationVertical);
+                sv.setAlignment_(cocoa::NSLayoutAttributeLeading);
+                sv.setSpacing_(spacing as _);
+                if style.vertical_alignment != Alignment::Fill {
+                    // Make sure the vbox stays as small as its content.
+                    sv.setHuggingPriority_forOrientation_(
+                        NSLayoutPriorityDefaultHigh,
+                        cocoa::NSLayoutConstraintOrientationVertical,
+                    );
+                }
+            }
+            let renderer = ViewRenderer::new(rtl, sv, |parent, style, child| {
+                let gravity: cocoa::NSInteger = match style.vertical_alignment {
+                    Alignment::Start | Alignment::Fill => 1,
+                    Alignment::Center => 2,
+                    Alignment::End => 3,
+                };
+                let parent: cocoa::NSStackView = parent.try_into().unwrap();
+                unsafe { parent.addView_inGravity_(child, gravity) };
+            })
+            .ignore_vertical(true);
+            for item in items {
+                renderer.render(item);
+            }
+            sv.into()
+        }
+        HBox(model::HBox {
+            mut items,
+            spacing,
+            affirmative_order,
+        }) => {
+            if affirmative_order {
+                items.reverse();
+            }
+            let sv = unsafe { StrongRef::new(cocoa::NSStackView::alloc()) }.autorelease();
+            unsafe {
+                sv.init();
+                sv.setOrientation_(cocoa::NSUserInterfaceLayoutOrientationHorizontal);
+                sv.setAlignment_(cocoa::NSLayoutAttributeTop);
+                sv.setSpacing_(spacing as _);
+                if style.horizontal_alignment != Alignment::Fill {
+                    // Make sure the hbox stays as small as its content.
+                    sv.setHuggingPriority_forOrientation_(
+                        NSLayoutPriorityDefaultHigh,
+                        cocoa::NSLayoutConstraintOrientationHorizontal,
+                    );
+                }
+            }
+            let renderer = ViewRenderer::new(rtl, sv, |parent, style, child| {
+                let gravity: cocoa::NSInteger = match style.horizontal_alignment {
+                    Alignment::Start | Alignment::Fill => 1,
+                    Alignment::Center => 2,
+                    Alignment::End => 3,
+                };
+                let parent: cocoa::NSStackView = parent.try_into().unwrap();
+                unsafe { parent.addView_inGravity_(child, gravity) };
+            })
+            .ignore_horizontal(true);
+            for item in items {
+                renderer.render(item);
+            }
+            sv.into()
+        }
+        Button(mut b) => {
+            if let Some(Label(model::Label {
+                text: Property::Static(text),
+                ..
+            })) = b.content.take().map(|e| e.element_type)
+            {
+                let button = self::Button { element: b }.with_title(text.as_str());
+                button.into()
+            } else {
+                return None;
+            }
+        }
+        Checkbox(cb) => {
+            let button = self::Checkbox { element: cb }.into_button();
+            button.into()
+        }
+        Label(model::Label { text, bold }) => {
+            let tf = cocoa::NSTextField(unsafe {
+                cocoa::NSTextField::wrappingLabelWithString_(nsstring(""))
+            });
+            unsafe { tf.setSelectable_(runtime::NO) };
+            if bold {
+                unsafe { tf.setFont_(cocoa::NSFont::boldSystemFontOfSize_(0.0)) };
+            }
+            match text {
+                Property::Static(text) => {
+                    unsafe { tf.setStringValue_(nsstring(text.as_str())) };
+                }
+                Property::Binding(b) => {
+                    unsafe { tf.setStringValue_(nsstring(b.borrow().as_str())) };
+                    b.on_change(move |s| unsafe { tf.setStringValue_(nsstring(s)) });
+                }
+                Property::ReadOnly(_) => unimplemented!("ReadOnly not supported for Label::text"),
+            }
+            tf.into()
+        }
+        Progress(model::Progress { amount }) => {
+            fn update(progress: cocoa::NSProgressIndicator, value: Option<f32>) {
+                unsafe {
+                    match value {
+                        None => {
+                            progress.setIndeterminate_(runtime::YES);
+                            progress.startAnimation_(progress.0);
+                        }
+                        Some(v) => {
+                            progress.setDoubleValue_(v as f64);
+                            progress.setIndeterminate_(runtime::NO);
+                        }
+                    }
+                }
+            }
+
+            let progress = unsafe { StrongRef::new(cocoa::NSProgressIndicator::alloc()) };
+            unsafe {
+                progress.init();
+                progress.setMinValue_(0.0);
+                progress.setMaxValue_(1.0);
+            }
+            match amount {
+                Property::Static(v) => update(*progress, v),
+                Property::Binding(s) => {
+                    update(*progress, *s.borrow());
+                    let weak = progress.weak();
+                    s.on_change(move |v| {
+                        if let Some(r) = weak.lock() {
+                            update(*r, *v);
+                        }
+                    });
+                }
+                Property::ReadOnly(_) => (),
+            }
+            progress.autorelease().into()
+        }
+        Scroll(model::Scroll { content }) => {
+            let sv = unsafe { StrongRef::new(cocoa::NSScrollView::alloc()) }.autorelease();
+            unsafe {
+                sv.init();
+                sv.setHasVerticalScroller_(runtime::YES);
+            }
+            if let Some(content) = content {
+                ViewRenderer::new_with_selector(rtl, sv, sel!(setDocumentView:))
+                    .ignore_vertical(true)
+                    .render(*content);
+            }
+            sv.into()
+        }
+        TextBox(model::TextBox {
+            placeholder,
+            content,
+            editable,
+        }) => {
+            let tv: StrongRef<cocoa::NSTextView> = TextView.into_object().cast();
+            unsafe {
+                tv.setEditable_(editable.into());
+
+                cocoa::NSTextView_NSSharing::setAllowsUndo_(&*tv, runtime::YES);
+                tv.setVerticallyResizable_(runtime::YES);
+                if rtl {
+                    let ps = StrongRef::new(cocoa::NSMutableParagraphStyle::alloc());
+                    ps.init();
+                    ps.setAlignment_(cocoa::NSTextAlignmentRight);
+                    // We don't `use cocoa::NSTextView_NSSharing` because it has some methods which
+                    // conflict with others that make it inconvenient.
+                    cocoa::NSTextView_NSSharing::setDefaultParagraphStyle_(&*tv, (*ps).into());
+                }
+                {
+                    let container = tv.textContainer();
+                    container.setSize_(cocoa::NSSize {
+                        width: f64::MAX,
+                        height: f64::MAX,
+                    });
+                    container.setWidthTracksTextView_(runtime::YES);
+                }
+                if let Some(placeholder) = placeholder {
+                    // It's unclear why dictionaryWithObject_forKey_ takes `u64` rather than `id`
+                    // arguments.
+                    let attrs = cocoa::NSDictionary(
+                        <cocoa::NSDictionary as NSDictionary_NSDictionaryCreation<
+                            cocoa::NSAttributedStringKey,
+                            cocoa::id,
+                        >>::dictionaryWithObject_forKey_(
+                            cocoa::NSColor::placeholderTextColor().0 as u64,
+                            cocoa::NSForegroundColorAttributeName.0 as u64,
+                        ),
+                    );
+                    let string = StrongRef::new(cocoa::NSAttributedString(
+                        cocoa::NSAttributedString::alloc()
+                            .initWithString_attributes_(nsstring(placeholder.as_str()), attrs),
+                    ));
+                    // XXX: `setPlaceholderAttributedString` is undocumented (discovered at
+                    // https://stackoverflow.com/a/43028577 and works identically to NSTextField),
+                    // though hopefully it will be exposed in a public API some day.
+                    tv.performSelector_withObject_(sel!(setPlaceholderAttributedString:), string.0);
+                }
+            }
+            match content {
+                Property::Static(s) => unsafe { tv.setString_(nsstring(s.as_str())) },
+                Property::ReadOnly(od) => {
+                    let weak = tv.weak();
+                    od.register(move |s| {
+                        if let Some(tv) = weak.lock() {
+                            *s = read_nsstring(unsafe { tv.string() });
+                        }
+                    });
+                }
+                Property::Binding(b) => {
+                    let weak = tv.weak();
+                    b.on_change(move |s| {
+                        if let Some(tv) = weak.lock() {
+                            unsafe { tv.setString_(nsstring(s.as_str())) };
+                        }
+                    });
+                    unsafe { tv.setString_(nsstring(b.borrow().as_str())) };
+                }
+            }
+            tv.autorelease().into()
+        }
+    })
+}
diff --git a/toolkit/crashreporter/client/app/src/ui/macos/objc.rs b/toolkit/crashreporter/client/app/src/ui/macos/objc.rs
new file mode 100644
index 0000000000..d4f3f1c419
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/ui/macos/objc.rs
@@ -0,0 +1,242 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Objective-C bindings and helpers.
+
+// Forward all exports from the `objc` crate.
+pub use objc::*;
+
+/// An objc class instance which contains rust data `T`.
+#[derive(Clone, Copy)]
+#[repr(transparent)]
+pub struct Objc<T> {
+    pub instance: cocoa::id,
+    _phantom: std::marker::PhantomData<*mut T>,
+}
+
+impl<T> Objc<T> {
+    pub fn new(instance: cocoa::id) -> Self {
+        Objc {
+            instance,
+            _phantom: std::marker::PhantomData,
+        }
+    }
+
+    pub fn data(&self) -> &T {
+        let data = *unsafe { (*self.instance).get_ivar::<usize>("rust_self") } as *mut T;
+        unsafe { &*data }
+    }
+
+    pub fn data_mut(&mut self) -> &mut T {
+        let data = *unsafe { (*self.instance).get_ivar::<usize>("rust_self") } as *mut T;
+        unsafe { &mut *data }
+    }
+}
+
+impl<T> std::ops::Deref for Objc<T> {
+    type Target = T;
+    fn deref(&self) -> &Self::Target {
+        self.data()
+    }
+}
+
+impl<T> std::ops::DerefMut for Objc<T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        self.data_mut()
+    }
+}
+
+unsafe impl<T> Encode for Objc<T> {
+    fn encode() -> Encoding {
+        cocoa::id::encode()
+    }
+}
+
+/// Wrapper to provide `Encode` for bindgen-generated types (bindgen should do this in the future).
+#[repr(transparent)]
+pub struct Ptr<T>(pub T);
+
+unsafe impl<T> Encode for Ptr<T> {
+    fn encode() -> Encoding {
+        cocoa::id::encode()
+    }
+}
+
+/// A strong objective-c reference to `T`.
+#[repr(transparent)]
+pub struct StrongRef<T> {
+    ptr: rc::StrongPtr,
+    _phantom: std::marker::PhantomData<T>,
+}
+
+impl<T> Clone for StrongRef<T> {
+    fn clone(&self) -> Self {
+        StrongRef {
+            ptr: self.ptr.clone(),
+            _phantom: self._phantom,
+        }
+    }
+}
+
+impl<T> std::ops::Deref for StrongRef<T> {
+    type Target = T;
+    fn deref(&self) -> &Self::Target {
+        let obj: &cocoa::id = &*self.ptr;
+        unsafe { std::mem::transmute(obj) }
+    }
+}
+
+impl<T> StrongRef<T> {
+    /// Assume the given pointer-wrapper is an already-retained strong reference.
+    ///
+    /// # Safety
+    /// The type _must_ be the same size as cocoa::id and contain only a cocoa::id.
+    pub unsafe fn new(v: T) -> Self {
+        std::mem::transmute_copy(&v)
+    }
+
+    /// Retain the given pointer-wrapper.
+    ///
+    /// # Safety
+    /// The type _must_ be the same size as cocoa::id and contain only a cocoa::id.
+    #[allow(dead_code)]
+    pub unsafe fn retain(v: T) -> Self {
+        let obj: cocoa::id = std::mem::transmute_copy(&v);
+        StrongRef {
+            ptr: rc::StrongPtr::retain(obj),
+            _phantom: std::marker::PhantomData,
+        }
+    }
+
+    pub fn autorelease(self) -> T {
+        let obj = self.ptr.autorelease();
+        unsafe { std::mem::transmute_copy(&obj) }
+    }
+
+    pub fn weak(&self) -> WeakRef<T> {
+        WeakRef {
+            ptr: self.ptr.weak(),
+            _phantom: std::marker::PhantomData,
+        }
+    }
+
+    /// Unwrap the StrongRef value without affecting reference counts.
+    ///
+    /// This is the opposite of `new`.
+    #[allow(dead_code)]
+    pub fn unwrap(self: Self) -> T {
+        let v = unsafe { std::mem::transmute_copy(&self) };
+        std::mem::forget(self);
+        v
+    }
+
+    /// Cast to a base class.
+    ///
+    /// Bindgen pointer-wrappers have trival `From<Derived> for Base` implementations.
+    pub fn cast<U: From<T>>(self) -> StrongRef<U> {
+        StrongRef {
+            ptr: self.ptr,
+            _phantom: std::marker::PhantomData,
+        }
+    }
+}
+
+/// A weak objective-c reference to `T`.
+#[derive(Clone)]
+#[repr(transparent)]
+pub struct WeakRef<T> {
+    ptr: rc::WeakPtr,
+    _phantom: std::marker::PhantomData<T>,
+}
+
+impl<T> WeakRef<T> {
+    pub fn lock(&self) -> Option<StrongRef<T>> {
+        let ptr = self.ptr.load();
+        if ptr.is_null() {
+            None
+        } else {
+            Some(StrongRef {
+                ptr,
+                _phantom: std::marker::PhantomData,
+            })
+        }
+    }
+}
+
+/// A macro for creating an objc class.
+///
+/// Classes _must_ be registered before use (`Objc<T>::register()`).
+///
+/// Example:
+/// ```
+/// struct Foo(u8);
+///
+/// objc_class! {
+///     impl Foo: NSObject {
+///         #[sel(mySelector:)]
+///         fn my_selector(&mut self, arg: u8) -> u8 {
+///             self.0 + arg
+///         }
+///     }
+/// }
+///
+/// fn make_foo() -> StrongRef<Objc<Foo>> {
+///     Foo(42).into_object()
+/// }
+/// ```
+///
+/// Call `T::into_object()` to create the objective-c class instance.
+macro_rules! objc_class {
+    ( impl $name:ident : $base:ident $(<$($protocol:ident),+>)? {
+        $(
+            #[sel($($sel:tt)+)]
+            fn $mname:ident (&mut $self:ident $(, $argname:ident : $argtype:ty )*) $(-> $rettype:ty)? $body:block
+        )*
+    }) => {
+        impl Objc<$name> {
+            pub fn register() {
+                let mut decl = declare::ClassDecl::new(concat!("CR", stringify!($name)), class!($base)).expect(concat!("failed to declare ", stringify!($name), " class"));
+                $($(decl.add_protocol(runtime::Protocol::get(stringify!($protocol)).expect(concat!("failed to find ",stringify!($protocol)," protocol")));)+)?
+                decl.add_ivar::<usize>("rust_self");
+                $({
+                    extern fn method_impl(obj: &mut runtime::Object, _: runtime::Sel $(, $argname: $argtype )*) $(-> $rettype)? {
+                        Objc::<$name>::new(obj).$mname($($argname),*)
+                    }
+                    unsafe {
+                        decl.add_method(sel!($($sel)+), method_impl as extern fn(&mut runtime::Object, runtime::Sel $(, $argname: $argtype )*) $(-> $rettype)?);
+                    }
+                })*
+                {
+                    extern fn dealloc_impl(obj: &runtime::Object, _: runtime::Sel) {
+                        drop(unsafe { Box::from_raw(*obj.get_ivar::<usize>("rust_self") as *mut $name) });
+                        unsafe {
+                            let _: () = msg_send![super(obj, class!(NSObject)), dealloc];
+                        }
+                    }
+                    unsafe {
+                        decl.add_method(sel!(dealloc), dealloc_impl as extern fn(&runtime::Object, runtime::Sel));
+                    }
+                }
+                decl.register();
+            }
+
+            pub fn class() -> &'static runtime::Class {
+                runtime::Class::get(concat!("CR", stringify!($name))).expect("class not registered")
+            }
+
+            $(fn $mname (&mut $self $(, $argname : $argtype )*) $(-> $rettype)? $body)*
+        }
+
+        impl $name {
+            pub fn into_object(self) -> StrongRef<Objc<$name>> {
+                let obj: *mut runtime::Object = unsafe { msg_send![Objc::<Self>::class(), alloc] };
+                unsafe { (*obj).set_ivar("rust_self", Box::into_raw(Box::new(self)) as usize) };
+                let obj: *mut runtime::Object = unsafe { msg_send![obj, init] };
+                unsafe { StrongRef::new(Objc::new(obj)) }
+            }
+        }
+    }
+}
+
+pub(crate) use objc_class;
diff --git a/toolkit/crashreporter/client/app/src/ui/macos/plist.rs b/toolkit/crashreporter/client/app/src/ui/macos/plist.rs
new file mode 100644
index 0000000000..a5bbe0aa0a
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/ui/macos/plist.rs
@@ -0,0 +1,44 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! The embedded Info.plist file.
+
+const DATA: &[u8] = br#"<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>CFBundleDevelopmentRegion</key>
+	<string>English</string>
+	<key>CFBundleDisplayName</key>
+	<string>Crash Reporter</string>
+	<key>CFBundleExecutable</key>
+	<string>crashreporter</string>
+	<key>CFBundleIdentifier</key>
+	<string>org.mozilla.crashreporter</string>
+	<key>CFBundleInfoDictionaryVersion</key>
+	<string>6.0</string>
+	<key>CFBundleName</key>
+	<string>Crash Reporter</string>
+	<key>CFBundlePackageType</key>
+	<string>APPL</string>
+	<key>CFBundleVersion</key>
+	<string>1.0</string>
+	<key>LSHasLocalizedDisplayName</key>
+	<true/>
+	<key>NSRequiresAquaSystemAppearance</key>
+	<false/>
+	<key>NSPrincipalClass</key>
+	<string>NSApplication</string>
+</dict>
+</plist>"#;
+
+const N: usize = DATA.len();
+
+const PTR: *const [u8; N] = DATA.as_ptr() as *const [u8; N];
+
+#[used]
+#[link_section = "__TEXT,__info_plist"]
+// # Safety
+// The array pointer is created from `DATA` (a slice pointer) with `DATA.len()` as the length.
+static PLIST: [u8; N] = unsafe { *PTR };
diff --git a/toolkit/crashreporter/client/app/src/ui/mod.rs b/toolkit/crashreporter/client/app/src/ui/mod.rs
new file mode 100644
index 0000000000..8464b6a9b3
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/ui/mod.rs
@@ -0,0 +1,295 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! The UI model, UI implementations, and functions using them.
+//!
+//! UIs must implement:
+//! * a `fn run_loop(&self, app: model::Application)` method which should display the UI and block while
+//!   handling events until the application terminates,
+//! * a `fn invoke(&self, f: model::InvokeFn)` method which invokes the given function
+//!   asynchronously (without blocking) on the UI loop thread.
+
+use crate::std::{rc::Rc, sync::Arc};
+use crate::{
+    async_task::AsyncTask, config::Config, data, logic::ReportCrash, settings::Settings, std,
+    thread_bound::ThreadBound,
+};
+use model::{ui, Application};
+use ui_impl::UI;
+
+mod model;
+
+#[cfg(all(not(test), any(target_os = "linux", target_os = "windows")))]
+mod icon {
+    // Must be DWORD-aligned for Win32 CreateIconFromResource.
+    #[repr(align(4))]
+    struct Aligned<Bytes: ?Sized>(Bytes);
+    static PNG_DATA_ALIGNMENT: &'static Aligned<[u8]> =
+        &Aligned(*include_bytes!("crashreporter.png"));
+    pub static PNG_DATA: &'static [u8] = &PNG_DATA_ALIGNMENT.0;
+}
+
+#[cfg(test)]
+pub mod test {
+    pub mod model {
+        pub use crate::ui::model::*;
+    }
+}
+
+cfg_if::cfg_if! {
+    if #[cfg(test)] {
+        #[path = "test.rs"]
+        pub mod ui_impl;
+    } else if #[cfg(target_os = "linux")] {
+        #[path = "gtk.rs"]
+        mod ui_impl;
+    } else if #[cfg(target_os = "windows")] {
+        #[path = "windows/mod.rs"]
+        mod ui_impl;
+    } else if #[cfg(target_os = "macos")] {
+        #[path = "macos/mod.rs"]
+        mod ui_impl;
+    } else {
+        mod ui_impl {
+            #[derive(Default)]
+            pub struct UI;
+
+            impl UI {
+                pub fn run_loop(&self, _app: super::model::Application) {
+                    unimplemented!();
+                }
+
+                pub fn invoke(&self, _f: super::model::InvokeFn) {
+                    unimplemented!();
+                }
+            }
+        }
+    }
+}
+
+/// Display an error dialog with the given message.
+#[cfg_attr(mock, allow(unused))]
+pub fn error_dialog<M: std::fmt::Display>(config: &Config, message: M) {
+    let close = data::Event::default();
+    // Config may not have localized strings
+    let string_or = |name, fallback: &str| {
+        if config.strings.is_none() {
+            fallback.into()
+        } else {
+            config.string(name)
+        }
+    };
+
+    let details = if config.strings.is_none() {
+        format!("Details: {}", message)
+    } else {
+        config
+            .build_string("crashreporter-error-details")
+            .arg("details", message.to_string())
+            .get()
+    };
+
+    let window = ui! {
+        Window title(string_or("crashreporter-branded-title", "Firefox Crash Reporter")) hsize(600) vsize(400)
+            close_when(&close) halign(Alignment::Fill) valign(Alignment::Fill) {
+            VBox margin(10) spacing(10) halign(Alignment::Fill) valign(Alignment::Fill) {
+                Label text(string_or(
+                        "crashreporter-error",
+                        "The application had a problem and crashed. \
+                        Unfortunately, the crash reporter is unable to submit a report for the crash."
+                )),
+                Label text(details),
+                Button["close"] halign(Alignment::End) on_click(move || close.fire(&())) {
+                    Label text(string_or("crashreporter-button-close", "Close"))
+                }
+            }
+        }
+    };
+
+    UI::default().run_loop(Application {
+        windows: vec![window],
+        rtl: config.is_rtl(),
+    });
+}
+
+#[derive(Default, Debug, PartialEq, Eq)]
+pub enum SubmitState {
+    #[default]
+    Initial,
+    InProgress,
+    Success,
+    Failure,
+}
+
+/// The UI for the main crash reporter windows.
+pub struct ReportCrashUI {
+    state: Arc<ThreadBound<ReportCrashUIState>>,
+    ui: Arc<UI>,
+    config: Arc<Config>,
+    logic: Rc<AsyncTask<ReportCrash>>,
+}
+
+/// The state of the creash UI.
+pub struct ReportCrashUIState {
+    pub send_report: data::Synchronized<bool>,
+    pub include_address: data::Synchronized<bool>,
+    pub show_details: data::Synchronized<bool>,
+    pub details: data::Synchronized<String>,
+    pub comment: data::OnDemand<String>,
+    pub submit_state: data::Synchronized<SubmitState>,
+    pub close_window: data::Event<()>,
+}
+
+impl ReportCrashUI {
+    pub fn new(
+        initial_settings: &Settings,
+        config: Arc<Config>,
+        logic: AsyncTask<ReportCrash>,
+    ) -> Self {
+        let send_report = data::Synchronized::new(initial_settings.submit_report);
+        let include_address = data::Synchronized::new(initial_settings.include_url);
+
+        ReportCrashUI {
+            state: Arc::new(ThreadBound::new(ReportCrashUIState {
+                send_report,
+                include_address,
+                show_details: Default::default(),
+                details: Default::default(),
+                comment: Default::default(),
+                submit_state: Default::default(),
+                close_window: Default::default(),
+            })),
+            ui: Default::default(),
+            config,
+            logic: Rc::new(logic),
+        }
+    }
+
+    pub fn async_task(&self) -> AsyncTask<ReportCrashUIState> {
+        let state = self.state.clone();
+        let ui = Arc::downgrade(&self.ui);
+        AsyncTask::new(move |f| {
+            let Some(ui) = ui.upgrade() else { return };
+            ui.invoke(Box::new(cc! { (state) move || {
+                f(state.borrow());
+            }}));
+        })
+    }
+
+    pub fn run(&self) {
+        let ReportCrashUI {
+            state,
+            ui,
+            config,
+            logic,
+        } = self;
+        let ReportCrashUIState {
+            send_report,
+            include_address,
+            show_details,
+            details,
+            comment,
+            submit_state,
+            close_window,
+        } = state.borrow();
+
+        send_report.on_change(cc! { (logic) move |v| {
+            let v = *v;
+            logic.push(move |s| s.settings.borrow_mut().submit_report = v);
+        }});
+        include_address.on_change(cc! { (logic) move |v| {
+            let v = *v;
+            logic.push(move |s| s.settings.borrow_mut().include_url = v);
+        }});
+
+        let input_enabled = submit_state.mapped(|s| s == &SubmitState::Initial);
+        let send_report_and_input_enabled =
+            data::Synchronized::join(send_report, &input_enabled, |s, e| *s && *e);
+
+        let submit_status_text = submit_state.mapped(cc! { (config) move |s| {
+            config.string(match s {
+                SubmitState::Initial => "crashreporter-submit-status",
+                SubmitState::InProgress => "crashreporter-submit-in-progress",
+                SubmitState::Success => "crashreporter-submit-success",
+                SubmitState::Failure => "crashreporter-submit-failure",
+            })
+        }});
+
+        let progress_visible = submit_state.mapped(|s| s == &SubmitState::InProgress);
+
+        let details_window = ui! {
+            Window["crash-details-window"] title(config.string("crashreporter-view-report-title"))
+                visible(show_details) modal(true) hsize(600) vsize(400)
+                halign(Alignment::Fill) valign(Alignment::Fill)
+            {
+                VBox margin(10) spacing(10) halign(Alignment::Fill) valign(Alignment::Fill) {
+                    Scroll halign(Alignment::Fill) valign(Alignment::Fill) {
+                        TextBox["details-text"] content(details) halign(Alignment::Fill) valign(Alignment::Fill)
+                    },
+                    Button["close-details"] halign(Alignment::End) on_click(cc! { (show_details) move || *show_details.borrow_mut() = false }) {
+                        Label text(config.string("crashreporter-button-ok"))
+                    }
+                }
+            }
+        };
+
+        let main_window = ui! {
+            Window title(config.string("crashreporter-branded-title")) hsize(600) vsize(400)
+                halign(Alignment::Fill) valign(Alignment::Fill) close_when(close_window)
+                child_window(details_window)
+            {
+                VBox margin(10) spacing(10) halign(Alignment::Fill) valign(Alignment::Fill) {
+                    Label text(config.string("crashreporter-apology")) bold(true),
+                    Label text(config.string("crashreporter-crashed-and-restore")),
+                    Label text(config.string("crashreporter-plea")),
+                    Checkbox["send"] checked(send_report) label(config.string("crashreporter-send-report"))
+                        enabled(&input_enabled),
+                    VBox margin_start(20) spacing(5) halign(Alignment::Fill) valign(Alignment::Fill) {
+                        Button["details"] enabled(&send_report_and_input_enabled) on_click(cc! { (config, details, show_details, logic) move || {
+                                // Immediately display the window to feel responsive, even if forming
+                                // the details string takes a little while (it really shouldn't
+                                // though).
+                                *details.borrow_mut() = config.string("crashreporter-loading-details");
+                                logic.push(|s| s.update_details());
+                                *show_details.borrow_mut() = true;
+                            }})
+                        {
+                            Label text(config.string("crashreporter-button-details"))
+                        },
+                        Scroll halign(Alignment::Fill) valign(Alignment::Fill) {
+                            TextBox["comment"] placeholder(config.string("crashreporter-comment-prompt"))
+                                content(comment)
+                                editable(true)
+                                enabled(&send_report_and_input_enabled)
+                                halign(Alignment::Fill) valign(Alignment::Fill)
+                        },
+                        Checkbox["include-url"] checked(include_address)
+                            label(config.string("crashreporter-include-url")) enabled(&send_report_and_input_enabled),
+                        Label text(&submit_status_text) margin_top(20),
+                        Progress halign(Alignment::Fill) visible(&progress_visible),
+                    },
+                    HBox valign(Alignment::End) halign(Alignment::End) spacing(10) affirmative_order(true)
+                    {
+                        Button["restart"] visible(config.restart_command.is_some())
+                            on_click(cc! { (logic) move || logic.push(|s| s.restart()) })
+                            enabled(&input_enabled) hsize(160)
+                        {
+                            Label text(config.string("crashreporter-button-restart"))
+                        },
+                        Button["quit"] on_click(cc! { (logic) move || logic.push(|s| s.quit()) })
+                            enabled(&input_enabled) hsize(160)
+                        {
+                            Label text(config.string("crashreporter-button-quit"))
+                        }
+                    }
+                }
+            }
+        };
+
+        ui.run_loop(Application {
+            windows: vec![main_window],
+            rtl: config.is_rtl(),
+        });
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/ui/model/button.rs b/toolkit/crashreporter/client/app/src/ui/model/button.rs
new file mode 100644
index 0000000000..d522fad6fc
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/ui/model/button.rs
@@ -0,0 +1,26 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use super::{Element, ElementBuilder};
+use crate::data::Event;
+
+/// A clickable button.
+#[derive(Default, Debug)]
+pub struct Button {
+    pub content: Option<Box<Element>>,
+    pub click: Event<()>,
+}
+
+impl ElementBuilder<Button> {
+    pub fn on_click<F>(&mut self, f: F)
+    where
+        F: Fn() + 'static,
+    {
+        self.element_type.click.subscribe(move |_| f());
+    }
+
+    pub fn add_child(&mut self, child: Element) {
+        Self::single_child(&mut self.element_type.content, child);
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/ui/model/checkbox.rs b/toolkit/crashreporter/client/app/src/ui/model/checkbox.rs
new file mode 100644
index 0000000000..8923e33558
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/ui/model/checkbox.rs
@@ -0,0 +1,22 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use crate::data::Property;
+
+/// A checkbox (with optional label).
+#[derive(Default, Debug)]
+pub struct Checkbox {
+    pub checked: Property<bool>,
+    pub label: Option<String>,
+}
+
+impl super::ElementBuilder<Checkbox> {
+    pub fn checked(&mut self, value: impl Into<Property<bool>>) {
+        self.element_type.checked = value.into();
+    }
+
+    pub fn label<S: Into<String>>(&mut self, label: S) {
+        self.element_type.label = Some(label.into());
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/ui/model/hbox.rs b/toolkit/crashreporter/client/app/src/ui/model/hbox.rs
new file mode 100644
index 0000000000..b6c0e27e8c
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/ui/model/hbox.rs
@@ -0,0 +1,34 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use super::{Element, ElementBuilder};
+
+/// A box which lays out contents horizontally.
+#[derive(Default, Debug)]
+pub struct HBox {
+    pub items: Vec<Element>,
+    pub spacing: u32,
+    pub affirmative_order: bool,
+}
+
+impl ElementBuilder<HBox> {
+    pub fn spacing(&mut self, value: u32) {
+        self.element_type.spacing = value;
+    }
+
+    /// Whether children are in affirmative order (and should be reordered based on platform
+    /// conventions).
+    ///
+    /// The children passed to `add_child` should be in most-affirmative to least-affirmative order
+    /// (e.g., "OK" then "Cancel" buttons).
+    ///
+    /// This is mainly useful for dialog buttons.
+    pub fn affirmative_order(&mut self, value: bool) {
+        self.element_type.affirmative_order = value;
+    }
+
+    pub fn add_child(&mut self, child: Element) {
+        self.element_type.items.push(child);
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/ui/model/label.rs b/toolkit/crashreporter/client/app/src/ui/model/label.rs
new file mode 100644
index 0000000000..096ce022e3
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/ui/model/label.rs
@@ -0,0 +1,22 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use crate::data::Property;
+
+/// A text label.
+#[derive(Debug, Default)]
+pub struct Label {
+    pub text: Property<String>,
+    pub bold: bool,
+}
+
+impl super::ElementBuilder<Label> {
+    pub fn text(&mut self, s: impl Into<Property<String>>) {
+        self.element_type.text = s.into();
+    }
+
+    pub fn bold(&mut self, value: bool) {
+        self.element_type.bold = value;
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/ui/model/mod.rs b/toolkit/crashreporter/client/app/src/ui/model/mod.rs
new file mode 100644
index 0000000000..5ea2ddc59a
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/ui/model/mod.rs
@@ -0,0 +1,344 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! The UI model.
+//!
+//! Model elements should generally be declared as types with all fields `pub` (to be accessed by
+//! UI implementations), though accessor methods are acceptable if needed. An
+//! `ElementBuilder<TYPE>` impl should be provided to create methods that will be used in the
+//! [`ui!`] macro. The model types are accessible when being _consumed_ by a UI implementation,
+//! whereas the `ElementBuilder` types are accessible when the model is being _created_.
+//!
+//! All elements should be listed in the `element_types!` macro in this file (note that [`Window`],
+//! while an element, isn't listed here as it cannot be a child element). This populates the
+//! `ElementType` enum and generates `From<Element>` for `ElementType`, and `TryFrom<ElementType>`
+//! for the element (as well as reference `TryFrom`).
+//!
+//! The model is written to accommodate layout and text direction differences (e.g. for RTL
+//! languages), and UI implementations are expected to account for this correctly.
+
+use crate::data::Property;
+pub use button::Button;
+pub use checkbox::Checkbox;
+pub use hbox::HBox;
+pub use label::Label;
+pub use progress::Progress;
+pub use scroll::Scroll;
+pub use textbox::TextBox;
+pub use vbox::VBox;
+pub use window::Window;
+
+mod button;
+mod checkbox;
+mod hbox;
+mod label;
+mod progress;
+mod scroll;
+mod textbox;
+mod vbox;
+mod window;
+
+/// A GUI element, including general style attributes and a more specific type.
+///
+/// `From<ElementBuilder<...>>` is implemented for all elements listed in `element_types!`.
+#[derive(Debug)]
+pub struct Element {
+    pub style: ElementStyle,
+    pub element_type: ElementType,
+}
+
+// This macro creates the `ElementType` enum and corresponding `From<ElementBuilder>` impls for
+// Element. The `ElementType` discriminants match the element type names.
+macro_rules! element_types {
+    ( $($name:ident),* ) => {
+        /// A type of GUI element.
+        #[derive(Debug)]
+        pub enum ElementType {
+            $($name($name)),*
+        }
+
+        $(
+        impl From<$name> for ElementType {
+            fn from(e: $name) -> ElementType {
+                ElementType::$name(e)
+            }
+        }
+
+        impl TryFrom<ElementType> for $name {
+            type Error = &'static str;
+
+            fn try_from(et: ElementType) -> Result<Self, Self::Error> {
+                if let ElementType::$name(v) = et {
+                    Ok(v)
+                } else {
+                    Err(concat!("ElementType was not ", stringify!($name)))
+                }
+            }
+        }
+
+        impl<'a> TryFrom<&'a ElementType> for &'a $name {
+            type Error = &'static str;
+
+            fn try_from(et: &'a ElementType) -> Result<Self, Self::Error> {
+                if let ElementType::$name(v) = et {
+                    Ok(v)
+                } else {
+                    Err(concat!("ElementType was not ", stringify!($name)))
+                }
+            }
+        }
+
+        impl From<ElementBuilder<$name>> for Element {
+             fn from(b: ElementBuilder<$name>) -> Self {
+                 Element {
+                     style: b.style,
+                     element_type: b.element_type.into(),
+                 }
+             }
+        }
+        )*
+    }
+}
+element_types! {
+    Button, Checkbox, HBox, Label, Progress, Scroll, TextBox, VBox
+}
+
+/// Common element style values.
+#[derive(Debug)]
+pub struct ElementStyle {
+    pub horizontal_alignment: Alignment,
+    pub vertical_alignment: Alignment,
+    pub horizontal_size_request: Option<u32>,
+    pub vertical_size_request: Option<u32>,
+    pub margin: Margin,
+    pub visible: Property<bool>,
+    pub enabled: Property<bool>,
+    #[cfg(test)]
+    pub id: Option<String>,
+}
+
+impl Default for ElementStyle {
+    fn default() -> Self {
+        ElementStyle {
+            horizontal_alignment: Default::default(),
+            vertical_alignment: Default::default(),
+            horizontal_size_request: Default::default(),
+            vertical_size_request: Default::default(),
+            margin: Default::default(),
+            visible: true.into(),
+            enabled: true.into(),
+            #[cfg(test)]
+            id: Default::default(),
+        }
+    }
+}
+
+/// A builder for `Element`s.
+///
+/// Each element should add an `impl ElementBuilder<TYPE>` to add methods to their builder.
+#[derive(Debug, Default)]
+pub struct ElementBuilder<T> {
+    pub style: ElementStyle,
+    pub element_type: T,
+}
+
+impl<T> ElementBuilder<T> {
+    /// Set horizontal alignment.
+    pub fn halign(&mut self, alignment: Alignment) {
+        self.style.horizontal_alignment = alignment;
+    }
+
+    /// Set vertical alignment.
+    pub fn valign(&mut self, alignment: Alignment) {
+        self.style.vertical_alignment = alignment;
+    }
+
+    /// Set the horizontal size request.
+    pub fn hsize(&mut self, value: u32) {
+        assert!(value <= i32::MAX as u32);
+        self.style.horizontal_size_request = Some(value);
+    }
+
+    /// Set the vertical size request.
+    pub fn vsize(&mut self, value: u32) {
+        assert!(value <= i32::MAX as u32);
+        self.style.vertical_size_request = Some(value);
+    }
+
+    /// Set start margin.
+    pub fn margin_start(&mut self, amount: u32) {
+        self.style.margin.start = amount;
+    }
+
+    /// Set end margin.
+    pub fn margin_end(&mut self, amount: u32) {
+        self.style.margin.end = amount;
+    }
+
+    /// Set start and end margins.
+    pub fn margin_horizontal(&mut self, amount: u32) {
+        self.margin_start(amount);
+        self.margin_end(amount)
+    }
+
+    /// Set top margin.
+    pub fn margin_top(&mut self, amount: u32) {
+        self.style.margin.top = amount;
+    }
+
+    /// Set bottom margin.
+    pub fn margin_bottom(&mut self, amount: u32) {
+        self.style.margin.bottom = amount;
+    }
+
+    /// Set top and bottom margins.
+    pub fn margin_vertical(&mut self, amount: u32) {
+        self.margin_top(amount);
+        self.margin_bottom(amount)
+    }
+
+    /// Set all margins.
+    pub fn margin(&mut self, amount: u32) {
+        self.margin_horizontal(amount);
+        self.margin_vertical(amount)
+    }
+
+    /// Set visibility.
+    pub fn visible(&mut self, value: impl Into<Property<bool>>) {
+        self.style.visible = value.into();
+    }
+
+    /// Set whether an element is enabled.
+    ///
+    /// This generally should enable/disable interaction with an element.
+    pub fn enabled(&mut self, value: impl Into<Property<bool>>) {
+        self.style.enabled = value.into();
+    }
+
+    /// Set the element identifier.
+    #[cfg(test)]
+    pub fn id(&mut self, value: impl Into<String>) {
+        self.style.id = Some(value.into());
+    }
+
+    /// Set the element identifier (stub).
+    #[cfg(not(test))]
+    pub fn id(&mut self, _value: impl Into<String>) {}
+
+    fn single_child(slot: &mut Option<Box<Element>>, child: Element) {
+        if slot.replace(Box::new(child)).is_some() {
+            panic!("{} can only have one child", std::any::type_name::<T>());
+        }
+    }
+}
+
+/// A typed [`Element`].
+///
+/// This is useful for the [`ui!`] macro when a method should accept a specific element type, since
+/// the macro always creates [`ElementBuilder<T>`](ElementBuilder) and ends with a `.into()` (and this implements
+/// `From<ElementBuilder<T>>`).
+#[derive(Debug, Default)]
+pub struct TypedElement<T> {
+    pub style: ElementStyle,
+    pub element_type: T,
+}
+
+impl<T> From<ElementBuilder<T>> for TypedElement<T> {
+    fn from(b: ElementBuilder<T>) -> Self {
+        TypedElement {
+            style: b.style,
+            element_type: b.element_type,
+        }
+    }
+}
+
+/// The alignment of an element in one direction.
+///
+/// Note that rather than `Left`/`Right`, this class has `Start`/`End` as it is meant to be
+/// layout-direction-aware.
+#[derive(Default, Debug, Clone, Copy, PartialEq, Eq)]
+#[allow(dead_code)]
+pub enum Alignment {
+    /// Align to the start of the direction.
+    #[default]
+    Start,
+    /// Align to the center of the direction.
+    Center,
+    /// Align to the end of the direction.
+    End,
+    /// Fill all available space.
+    Fill,
+}
+
+/// The margins of an element.
+///
+/// These are RTL-aware: for instance, `start` is the left margin in left-to-right languages and
+/// the right margin in right-to-left languages.
+#[derive(Default, Debug)]
+pub struct Margin {
+    pub start: u32,
+    pub end: u32,
+    pub top: u32,
+    pub bottom: u32,
+}
+
+/// A macro to allow a convenient syntax for creating elements.
+///
+/// The macro expects the following syntax:
+/// ```
+/// ElementTypeName some_method(arg1, arg2) other_method() {
+///     Child ...,
+///     Child2 ...
+/// }
+/// ```
+///
+/// The type is wrapped in an `ElementBuilder`, and methods are called on this builder with a
+/// mutable reference. This means that element types must implement Default and must implement
+/// builder methods on `ElementBuilder<ElementTypeName>`. The children block is optional, and calls
+/// `add_child(child: Element)` for each provided child (so implement this method if desired).
+///
+/// For testing, a string identifier can be set on any element with a `["my_identifier"]` following
+/// the element type.
+macro_rules! ui {
+    ( $el:ident
+        $([ $id:literal ])?
+        $( $method:ident $methodargs:tt )*
+        $({ $($contents:tt)* })?
+    ) => {
+        {
+            #[allow(unused_imports)]
+            use $crate::ui::model::*;
+            let mut el: ElementBuilder<$el> = Default::default();
+            $( el.id($id); )?
+            $( el.$method $methodargs ; )*
+            $( ui! { @children (el) $($contents)* } )?
+            el.into()
+        }
+    };
+    ( @children ($parent:expr) ) => {};
+    ( @children ($parent:expr)
+      $el:ident
+        $([ $id:literal ])?
+        $( $method:ident $methodargs:tt )*
+        $({ $($contents:tt)* })?
+      $(, $($rest:tt)* )?
+    ) => {
+        $parent.add_child(ui!( $el $([$id])? $( $method $methodargs )* $({ $($contents)* })? ));
+        $(ui!( @children ($parent) $($rest)* ))?
+    };
+}
+
+pub(crate) use ui;
+
+/// An application, defined as a set of windows.
+///
+/// When all windows are closed, the application is considered complete (and loops should exit).
+pub struct Application {
+    pub windows: Vec<TypedElement<Window>>,
+    /// Whether the text direction should be right-to-left.
+    pub rtl: bool,
+}
+
+/// A function to be invoked in the UI loop.
+pub type InvokeFn = Box<dyn FnOnce() + Send + 'static>;
diff --git a/toolkit/crashreporter/client/app/src/ui/model/progress.rs b/toolkit/crashreporter/client/app/src/ui/model/progress.rs
new file mode 100644
index 0000000000..f3e4e4bf77
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/ui/model/progress.rs
@@ -0,0 +1,19 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use crate::data::Property;
+
+/// A progress indicator.
+#[derive(Debug, Default)]
+pub struct Progress {
+    /// Progress between 0 and 1, or None if indeterminate.
+    pub amount: Property<Option<f32>>,
+}
+
+impl super::ElementBuilder<Progress> {
+    #[allow(dead_code)]
+    pub fn amount(&mut self, value: impl Into<Property<Option<f32>>>) {
+        self.element_type.amount = value.into();
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/ui/model/scroll.rs b/toolkit/crashreporter/client/app/src/ui/model/scroll.rs
new file mode 100644
index 0000000000..47efa4a81e
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/ui/model/scroll.rs
@@ -0,0 +1,17 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use super::{Element, ElementBuilder};
+
+/// A scrollable region.
+#[derive(Debug, Default)]
+pub struct Scroll {
+    pub content: Option<Box<Element>>,
+}
+
+impl ElementBuilder<Scroll> {
+    pub fn add_child(&mut self, child: Element) {
+        Self::single_child(&mut self.element_type.content, child);
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/ui/model/textbox.rs b/toolkit/crashreporter/client/app/src/ui/model/textbox.rs
new file mode 100644
index 0000000000..08cd9ca1bc
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/ui/model/textbox.rs
@@ -0,0 +1,27 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use crate::data::Property;
+
+/// A text box.
+#[derive(Debug, Default)]
+pub struct TextBox {
+    pub placeholder: Option<String>,
+    pub content: Property<String>,
+    pub editable: bool,
+}
+
+impl super::ElementBuilder<TextBox> {
+    pub fn placeholder(&mut self, text: impl Into<String>) {
+        self.element_type.placeholder = Some(text.into());
+    }
+
+    pub fn content(&mut self, value: impl Into<Property<String>>) {
+        self.element_type.content = value.into();
+    }
+
+    pub fn editable(&mut self, value: bool) {
+        self.element_type.editable = value;
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/ui/model/vbox.rs b/toolkit/crashreporter/client/app/src/ui/model/vbox.rs
new file mode 100644
index 0000000000..6f1b09b1e2
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/ui/model/vbox.rs
@@ -0,0 +1,22 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use super::{Element, ElementBuilder};
+
+/// A box which lays out contents vertically.
+#[derive(Debug, Default)]
+pub struct VBox {
+    pub items: Vec<Element>,
+    pub spacing: u32,
+}
+
+impl ElementBuilder<VBox> {
+    pub fn spacing(&mut self, value: u32) {
+        self.element_type.spacing = value;
+    }
+
+    pub fn add_child(&mut self, child: Element) {
+        self.element_type.items.push(child);
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/ui/model/window.rs b/toolkit/crashreporter/client/app/src/ui/model/window.rs
new file mode 100644
index 0000000000..b56071ca19
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/ui/model/window.rs
@@ -0,0 +1,46 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use super::{Element, ElementBuilder, TypedElement};
+use crate::data::Event;
+
+/// A window.
+#[derive(Debug, Default)]
+pub struct Window {
+    pub title: String,
+    /// The window content is the first element.
+    pub content: Option<Box<Element>>,
+    /// Logical child windows.
+    pub children: Vec<TypedElement<Self>>,
+    pub modal: bool,
+    pub close: Option<Event<()>>,
+}
+
+impl ElementBuilder<Window> {
+    /// Set the window title.
+    pub fn title(&mut self, s: impl Into<String>) {
+        self.element_type.title = s.into();
+    }
+
+    /// Set whether the window is modal (blocking interaction with other windows when displayed).
+    pub fn modal(&mut self, value: bool) {
+        self.element_type.modal = value;
+    }
+
+    /// Register an event to close the window.
+    pub fn close_when(&mut self, event: &Event<()>) {
+        self.element_type.close = Some(event.clone());
+    }
+
+    /// Add a window as a logical child of this one.
+    ///
+    /// Logical children are always displayed above their parents.
+    pub fn child_window(&mut self, window: TypedElement<Window>) {
+        self.element_type.children.push(window);
+    }
+
+    pub fn add_child(&mut self, child: Element) {
+        Self::single_child(&mut self.element_type.content, child);
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/ui/test.rs b/toolkit/crashreporter/client/app/src/ui/test.rs
new file mode 100644
index 0000000000..db98c072da
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/ui/test.rs
@@ -0,0 +1,270 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! A renderer for use in tests, which doesn't actually render a GUI but allows programmatic
+//! interaction.
+//!
+//! The [`ui!`](super::ui) macro supports labeling any element with a string identifier, which can
+//! be used to access the element in this UI.
+//!
+//! The [`Interact`] hook must be created to interact with the test UI, before the UI is run and on
+//! the same thread as the UI.
+//!
+//! See how this UI is used in [`crate::test`].
+
+use super::model::{self, Application, Element};
+use std::cell::RefCell;
+use std::collections::HashMap;
+use std::sync::{
+    atomic::{AtomicBool, AtomicU8, Ordering::Relaxed},
+    mpsc, Arc, Condvar, Mutex,
+};
+
+thread_local! {
+    static INTERACT: RefCell<Option<Arc<State>>> = Default::default();
+}
+
+/// A test UI which allows access to the UI elements.
+#[derive(Default)]
+pub struct UI {
+    interface: Mutex<Option<UIInterface>>,
+}
+
+impl UI {
+    pub fn run_loop(&self, app: Application) {
+        let (tx, rx) = mpsc::channel();
+        let interface = UIInterface { work: tx };
+
+        let elements = id_elements(&app);
+        INTERACT.with(cc! { (interface) move |r| {
+            if let Some(state) = &*r.borrow() {
+                state.set_interface(interface);
+            }
+        }});
+        *self.interface.lock().unwrap() = Some(interface.clone());
+
+        // Close the UI when the root windows are closed.
+        // Use a bitfield rather than a count in case the `close` event is fired multiple times.
+        assert!(app.windows.len() <= 8);
+        let mut windows = 0u8;
+        for i in 0..app.windows.len() {
+            windows |= 1 << i;
+        }
+        let windows = Arc::new(AtomicU8::new(windows));
+        for (index, window) in app.windows.iter().enumerate() {
+            if let Some(c) = &window.element_type.close {
+                c.subscribe(cc! { (interface, windows) move |&()| {
+                    let old = windows
+                        .fetch_update(Relaxed, Relaxed, |x| Some(x & !(1u8 << index)))
+                        .unwrap();
+                    if old == 1u8 << index {
+                        interface.work.send(Command::Finish).unwrap();
+                    }
+                }});
+            } else {
+                // No close event, so we must assume a closed state (and assume that _some_ window
+                // will have a close event registered so we don't drop the interface now).
+                windows
+                    .fetch_update(Relaxed, Relaxed, |x| Some(x & !(1u8 << index)))
+                    .unwrap();
+            }
+        }
+
+        while let Ok(f) = rx.recv() {
+            match f {
+                Command::Invoke(f) => f(),
+                Command::Interact(f) => f(&elements),
+                Command::Finish => break,
+            }
+        }
+
+        *self.interface.lock().unwrap() = None;
+        INTERACT.with(|r| {
+            if let Some(state) = &*r.borrow() {
+                state.clear_interface();
+            }
+        });
+    }
+
+    pub fn invoke(&self, f: model::InvokeFn) {
+        let guard = self.interface.lock().unwrap();
+        if let Some(interface) = &*guard {
+            let _ = interface.work.send(Command::Invoke(f));
+        }
+    }
+}
+
+/// Test interaction hook.
+#[derive(Clone)]
+pub struct Interact {
+    state: Arc<State>,
+}
+
+impl Interact {
+    /// Create an interaction hook for the test UI.
+    ///
+    /// This should be done before running the UI, and must be done on the same thread that
+    /// later runs it.
+    pub fn hook() -> Self {
+        let v = Interact {
+            state: Default::default(),
+        };
+        {
+            let state = v.state.clone();
+            INTERACT.with(move |r| *r.borrow_mut() = Some(state));
+        }
+        v
+    }
+
+    /// Wait for the render thread to be ready for interaction.
+    pub fn wait_for_ready(&self) {
+        let mut guard = self.state.interface.lock().unwrap();
+        while guard.is_none() && !self.state.cancel.load(Relaxed) {
+            guard = self.state.waiting_for_interface.wait(guard).unwrap();
+        }
+    }
+
+    /// Cancel an Interact (which causes `wait_for_ready` to always return).
+    pub fn cancel(&self) {
+        self.state.cancel.store(true, Relaxed);
+        self.state.waiting_for_interface.notify_all();
+    }
+
+    /// Run the given function on the element with the given type and identity.
+    ///
+    /// Panics if either the id is missing or the type is incorrect.
+    pub fn element<'a, 'b, T: 'b, F, R>(&self, id: &'a str, f: F) -> R
+    where
+        &'b T: TryFrom<&'b model::ElementType>,
+        F: FnOnce(&model::ElementStyle, &T) -> R + Send + 'a,
+        R: Send + 'a,
+    {
+        self.interact(id, move |element: &IdElement| match element {
+            IdElement::Generic(e) => Some(f(&e.style, (&e.element_type).try_into().ok()?)),
+            IdElement::Window(_) => None,
+        })
+        .expect("incorrect element type")
+    }
+
+    /// Run the given function on the window with the given identity.
+    ///
+    /// Panics if the id is missing or the type is incorrect.
+    pub fn window<'a, F, R>(&self, id: &'a str, f: F) -> R
+    where
+        F: FnOnce(&model::ElementStyle, &model::Window) -> R + Send + 'a,
+        R: Send + 'a,
+    {
+        self.interact(id, move |element| match element {
+            IdElement::Window(e) => Some(f(&e.style, &e.element_type)),
+            IdElement::Generic(_) => None,
+        })
+        .expect("incorrect element type")
+    }
+
+    fn interact<'a, 'b, F, R>(&self, id: &'a str, f: F) -> R
+    where
+        F: FnOnce(&IdElement<'b>) -> R + Send + 'a,
+        R: Send + 'a,
+    {
+        let (send, recv) = std::sync::mpsc::sync_channel(0);
+        {
+            let f: Box<dyn FnOnce(&IdElements<'b>) + Send + 'a> = Box::new(move |elements| {
+                let _ = send.send(elements.get(id).map(f));
+            });
+
+            // # Safety
+            // The function is run while `'a` is still valid (we wait here for it to complete).
+            let f: Box<dyn FnOnce(&IdElements) + Send + 'static> =
+                unsafe { std::mem::transmute(f) };
+
+            let guard = self.state.interface.lock().unwrap();
+            let interface = guard.as_ref().expect("renderer is not running");
+            let _ = interface.work.send(Command::Interact(f));
+        }
+        recv.recv().unwrap().expect("failed to get element")
+    }
+}
+
+#[derive(Clone)]
+struct UIInterface {
+    work: mpsc::Sender<Command>,
+}
+
+enum Command {
+    Invoke(Box<dyn FnOnce() + Send + 'static>),
+    Interact(Box<dyn FnOnce(&IdElements) + Send + 'static>),
+    Finish,
+}
+
+enum IdElement<'a> {
+    Generic(&'a Element),
+    Window(&'a model::TypedElement<model::Window>),
+}
+
+type IdElements<'a> = HashMap<String, IdElement<'a>>;
+
+#[derive(Default)]
+struct State {
+    interface: Mutex<Option<UIInterface>>,
+    waiting_for_interface: Condvar,
+    cancel: AtomicBool,
+}
+
+impl State {
+    /// Set the interface for the interaction client to use.
+    pub fn set_interface(&self, interface: UIInterface) {
+        *self.interface.lock().unwrap() = Some(interface);
+        self.waiting_for_interface.notify_all();
+    }
+
+    /// Clear the UI interface.
+    pub fn clear_interface(&self) {
+        *self.interface.lock().unwrap() = None;
+    }
+}
+
+fn id_elements<'a>(app: &'a Application) -> IdElements<'a> {
+    let mut elements: IdElements<'a> = Default::default();
+
+    let mut windows_to_visit: Vec<_> = app.windows.iter().collect();
+
+    let mut to_visit: Vec<&'a Element> = Vec::new();
+    while let Some(window) = windows_to_visit.pop() {
+        if let Some(id) = &window.style.id {
+            elements.insert(id.to_owned(), IdElement::Window(window));
+        }
+        windows_to_visit.extend(&window.element_type.children);
+
+        if let Some(content) = &window.element_type.content {
+            to_visit.push(content);
+        }
+    }
+
+    while let Some(el) = to_visit.pop() {
+        if let Some(id) = &el.style.id {
+            elements.insert(id.to_owned(), IdElement::Generic(el));
+        }
+
+        use model::ElementType::*;
+        match &el.element_type {
+            Button(model::Button {
+                content: Some(content),
+                ..
+            })
+            | Scroll(model::Scroll {
+                content: Some(content),
+            }) => {
+                to_visit.push(content);
+            }
+            VBox(model::VBox { items, .. }) | HBox(model::HBox { items, .. }) => {
+                for item in items {
+                    to_visit.push(item)
+                }
+            }
+            _ => (),
+        }
+    }
+
+    elements
+}
diff --git a/toolkit/crashreporter/client/app/src/ui/windows/font.rs b/toolkit/crashreporter/client/app/src/ui/windows/font.rs
new file mode 100644
index 0000000000..3ec48316eb
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/ui/windows/font.rs
@@ -0,0 +1,56 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use windows_sys::Win32::{Foundation::S_OK, Graphics::Gdi, UI::Controls};
+
+/// Windows font handle (`HFONT`).
+pub struct Font(Gdi::HFONT);
+
+impl Font {
+    /// Get the system theme caption font.
+    ///
+    /// Panics if the font cannot be retrieved.
+    pub fn caption() -> Self {
+        unsafe {
+            let mut font = std::mem::zeroed::<Gdi::LOGFONTW>();
+            success!(hresult
+                Controls::GetThemeSysFont(0, Controls::TMT_CAPTIONFONT as i32, &mut font)
+            );
+            Font(success!(pointer Gdi::CreateFontIndirectW(&font)))
+        }
+    }
+
+    /// Get the system theme bold caption font.
+    ///
+    /// Returns `None` if the font cannot be retrieved.
+    pub fn caption_bold() -> Option<Self> {
+        unsafe {
+            let mut font = std::mem::zeroed::<Gdi::LOGFONTW>();
+            if Controls::GetThemeSysFont(0, Controls::TMT_CAPTIONFONT as i32, &mut font) != S_OK {
+                return None;
+            }
+            font.lfWeight = Gdi::FW_BOLD as i32;
+
+            let ptr = Gdi::CreateFontIndirectW(&font);
+            if ptr == 0 {
+                return None;
+            }
+            Some(Font(ptr))
+        }
+    }
+}
+
+impl std::ops::Deref for Font {
+    type Target = Gdi::HFONT;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl Drop for Font {
+    fn drop(&mut self) {
+        unsafe { Gdi::DeleteObject(self.0 as _) };
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/ui/windows/gdi.rs b/toolkit/crashreporter/client/app/src/ui/windows/gdi.rs
new file mode 100644
index 0000000000..89828987bc
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/ui/windows/gdi.rs
@@ -0,0 +1,43 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! GDI helpers.
+
+use windows_sys::Win32::{
+    Foundation::HWND,
+    Graphics::Gdi::{self, GDI_ERROR, HDC, HGDIOBJ},
+};
+
+/// A GDI drawing context.
+pub struct DC {
+    hwnd: HWND,
+    hdc: HDC,
+}
+
+impl DC {
+    /// Create a new DC.
+    pub fn new(hwnd: HWND) -> Option<Self> {
+        let hdc = unsafe { Gdi::GetDC(hwnd) };
+        (hdc != 0).then_some(DC { hwnd, hdc })
+    }
+
+    /// Call the given function with a gdi object selected.
+    pub fn with_object_selected<R>(&self, object: HGDIOBJ, f: impl FnOnce(HDC) -> R) -> Option<R> {
+        let old_object = unsafe { Gdi::SelectObject(self.hdc, object) };
+        if old_object == 0 || old_object == GDI_ERROR as isize {
+            return None;
+        }
+        let ret = f(self.hdc);
+        // The prior object must be selected before releasing the DC. Ignore errors; this is
+        // best-effort.
+        unsafe { Gdi::SelectObject(self.hdc, old_object) };
+        Some(ret)
+    }
+}
+
+impl Drop for DC {
+    fn drop(&mut self) {
+        unsafe { Gdi::ReleaseDC(self.hwnd, self.hdc) };
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/ui/windows/layout.rs b/toolkit/crashreporter/client/app/src/ui/windows/layout.rs
new file mode 100644
index 0000000000..7563b6b2f0
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/ui/windows/layout.rs
@@ -0,0 +1,436 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Helpers for window layout.
+
+use super::{
+    model::{self, Alignment, Element, ElementStyle, Margin},
+    ElementRef, WideString,
+};
+use crate::data::Property;
+use std::collections::HashMap;
+use windows_sys::Win32::{
+    Foundation::{HWND, SIZE},
+    Graphics::Gdi,
+    UI::WindowsAndMessaging as win,
+};
+
+pub(super) type ElementMapping = HashMap<ElementRef, HWND>;
+
+/// Handles the layout of windows.
+///
+/// This is done in two passes. The first pass calculates the sizes for all elements in the tree.
+/// Once sizes are known, the second pass can appropriately position the elements (taking alignment
+/// into account).
+///
+/// Currently, the resize/reposition logic is tied into the methods here, which is an inconvenient
+/// design because when adding support for a new element type you have to add new information in
+/// disparate locations.
+pub struct Layout<'a> {
+    elements: &'a ElementMapping,
+    sizes: HashMap<ElementRef, Size>,
+    last_positioned: Option<HWND>,
+}
+
+// Unfortunately, there's no good way to get these margins. I just guessed and the first guesses
+// seemed to be close enough.
+const BUTTON_MARGIN: Margin = Margin {
+    start: 5,
+    end: 5,
+    top: 5,
+    bottom: 5,
+};
+const CHECKBOX_MARGIN: Margin = Margin {
+    start: 15,
+    end: 0,
+    top: 0,
+    bottom: 0,
+};
+
+impl<'a> Layout<'a> {
+    pub(super) fn new(elements: &'a ElementMapping) -> Self {
+        Layout {
+            elements,
+            sizes: Default::default(),
+            last_positioned: None,
+        }
+    }
+
+    /// Perform a layout of the element and all child elements.
+    pub fn layout(mut self, element: &Element, max_width: u32, max_height: u32) {
+        let max_size = Size {
+            width: max_width,
+            height: max_height,
+        };
+        self.resize(element, &max_size);
+        self.reposition(element, &Position::default(), &max_size);
+    }
+
+    fn resize(&mut self, element: &Element, max_size: &Size) -> Size {
+        let style = &element.style;
+
+        let mut inner_size = max_size.inner_size(style);
+        let mut content_size = None;
+
+        if !is_visible(style) {
+            self.sizes
+                .insert(ElementRef::new(element), Default::default());
+            return Default::default();
+        }
+
+        // Resize inner content.
+        //
+        // These cases should result in `content_size` being set, if relevant.
+        use model::ElementType::*;
+        match &element.element_type {
+            Button(model::Button {
+                content: Some(content),
+                ..
+            }) => {
+                // Special case for buttons with a label.
+                if let Label(model::Label {
+                    text: Property::Static(text),
+                    ..
+                }) = &content.element_type
+                {
+                    let mut size = inner_size.less_margin(&BUTTON_MARGIN);
+                    self.measure_text(text.as_str(), element, &mut size);
+                    content_size = Some(size.plus_margin(&BUTTON_MARGIN));
+                }
+            }
+            Checkbox(model::Checkbox {
+                label: Some(label), ..
+            }) => {
+                let mut size = inner_size.less_margin(&CHECKBOX_MARGIN);
+                self.measure_text(label.as_str(), element, &mut size);
+                content_size = Some(size.plus_margin(&CHECKBOX_MARGIN));
+            }
+            Label(model::Label { text, bold: _ }) => {
+                let mut size = inner_size.clone();
+                match text {
+                    Property::Static(text) => self.measure_text(text.as_str(), element, &mut size),
+                    Property::Binding(b) => {
+                        self.measure_text(b.borrow().as_str(), element, &mut size)
+                    }
+                    Property::ReadOnly(_) => {
+                        unimplemented!("Label::text does not support ReadOnly")
+                    }
+                }
+                content_size = Some(size);
+            }
+            VBox(model::VBox { items, spacing }) => {
+                let mut height = 0;
+                let mut max_width = 0;
+                let mut remaining_size = inner_size.clone();
+                let mut resize_child = |c| {
+                    let child_size = self.resize(c, &remaining_size);
+                    height += child_size.height;
+                    max_width = std::cmp::max(child_size.width, max_width);
+                    remaining_size.height = remaining_size
+                        .height
+                        .saturating_sub(child_size.height + spacing);
+                };
+                // First resize all non-Fill items; Fill items get the remaining space.
+                for item in items
+                    .iter()
+                    .filter(|i| i.style.vertical_alignment != Alignment::Fill)
+                {
+                    resize_child(item);
+                }
+                for item in items
+                    .iter()
+                    .filter(|i| i.style.vertical_alignment == Alignment::Fill)
+                {
+                    resize_child(item);
+                }
+                content_size = Some(Size {
+                    width: max_width,
+                    height: height + spacing * (items.len().saturating_sub(1) as u32),
+                });
+            }
+            HBox(model::HBox {
+                items,
+                spacing,
+                affirmative_order: _,
+            }) => {
+                let mut width = 0;
+                let mut max_height = 0;
+                let mut remaining_size = inner_size.clone();
+                let mut resize_child = |c| {
+                    let child_size = self.resize(c, &remaining_size);
+                    width += child_size.width;
+                    max_height = std::cmp::max(child_size.height, max_height);
+                    remaining_size.width = remaining_size
+                        .width
+                        .saturating_sub(child_size.width + spacing);
+                };
+                // First resize all non-Fill items; Fill items get the remaining space.
+                for item in items
+                    .iter()
+                    .filter(|i| i.style.horizontal_alignment != Alignment::Fill)
+                {
+                    resize_child(item);
+                }
+                for item in items
+                    .iter()
+                    .filter(|i| i.style.horizontal_alignment == Alignment::Fill)
+                {
+                    resize_child(item);
+                }
+                content_size = Some(Size {
+                    width: width + spacing * (items.len().saturating_sub(1) as u32),
+                    height: max_height,
+                });
+            }
+            Scroll(model::Scroll {
+                content: Some(content),
+            }) => {
+                content_size = Some(self.resize(content, &inner_size));
+            }
+            Progress(model::Progress { .. }) => {
+                // Min size recommended by windows uxguide
+                content_size = Some(Size {
+                    width: 160,
+                    height: 15,
+                });
+            }
+            // We don't support sizing by textbox content yet (need to read from the HWND due to
+            // Property::ReadOnly).
+            TextBox(_) => (),
+            _ => (),
+        }
+
+        // Adjust from content size.
+        if let Some(content_size) = content_size {
+            inner_size.from_content_size(style, &content_size);
+        }
+
+        // Compute/store (outer) size and return.
+        let size = inner_size.plus_margin(&style.margin);
+        self.sizes.insert(ElementRef::new(element), size);
+        size
+    }
+
+    fn get_size(&self, element: &Element) -> &Size {
+        self.sizes
+            .get(&ElementRef::new(element))
+            .expect("element not resized")
+    }
+
+    fn reposition(&mut self, element: &Element, position: &Position, parent_size: &Size) {
+        let style = &element.style;
+        if !is_visible(style) {
+            return;
+        }
+        let size = self.get_size(element);
+
+        let start_offset = match style.horizontal_alignment {
+            Alignment::Fill | Alignment::Start => 0,
+            Alignment::Center => parent_size.width.saturating_sub(size.width) / 2,
+            Alignment::End => parent_size.width.saturating_sub(size.width),
+        };
+        let top_offset = match style.vertical_alignment {
+            Alignment::Fill | Alignment::Start => 0,
+            Alignment::Center => parent_size.height.saturating_sub(size.height) / 2,
+            Alignment::End => parent_size.height.saturating_sub(size.height),
+        };
+
+        let inner_position = Position {
+            start: position.start + start_offset,
+            top: position.top + top_offset,
+        }
+        .less_margin(&style.margin);
+        let inner_size = size.less_margin(&style.margin);
+
+        // Set the window size/position if there is a handle associated with the element.
+        if let Some(&hwnd) = self.elements.get(&ElementRef::new(element)) {
+            unsafe {
+                win::SetWindowPos(
+                    hwnd,
+                    self.last_positioned.unwrap_or(win::HWND_TOP),
+                    inner_position.start.try_into().unwrap(),
+                    inner_position.top.try_into().unwrap(),
+                    inner_size.width.try_into().unwrap(),
+                    inner_size.height.try_into().unwrap(),
+                    0,
+                );
+                Gdi::InvalidateRect(hwnd, std::ptr::null(), 1);
+            }
+            self.last_positioned = Some(hwnd);
+        }
+
+        // Reposition content.
+        match &element.element_type {
+            model::ElementType::VBox(model::VBox { items, spacing }) => {
+                let mut position = inner_position;
+                let mut size = inner_size;
+                for item in items {
+                    self.reposition(item, &position, &size);
+                    let consumed = self.get_size(item).height + spacing;
+                    if item.style.vertical_alignment != Alignment::End {
+                        position.top += consumed;
+                    }
+                    size.height = size.height.saturating_sub(consumed);
+                }
+            }
+            model::ElementType::HBox(model::HBox {
+                items,
+                spacing,
+                // The default ordering matches the windows platform order
+                affirmative_order: _,
+            }) => {
+                let mut position = inner_position;
+                let mut size = inner_size;
+                for item in items {
+                    self.reposition(item, &position, &inner_size);
+                    let consumed = self.get_size(item).width + spacing;
+                    if item.style.horizontal_alignment != Alignment::End {
+                        position.start += consumed;
+                    }
+                    size.width = size.width.saturating_sub(consumed);
+                }
+            }
+            model::ElementType::Scroll(model::Scroll {
+                content: Some(content),
+            }) => {
+                self.reposition(content, &inner_position, &inner_size);
+            }
+            _ => (),
+        }
+    }
+
+    /// The `size` represents the maximum size permitted for the text (which is used for word
+    /// breaking), and it will be set to the precise width and height of the text. The width should
+    /// not exceed the input `size` width, but the height may.
+    fn measure_text(&mut self, text: &str, element: &Element, size: &mut Size) {
+        let Some(&window) = self.elements.get(&ElementRef::new(element)) else {
+            return;
+        };
+        let hdc = unsafe { Gdi::GetDC(window) };
+        unsafe { Gdi::SelectObject(hdc, win::SendMessageW(window, win::WM_GETFONT, 0, 0) as _) };
+        let mut height: u32 = 0;
+        let mut max_width: u32 = 0;
+        let mut char_fit = 0i32;
+        let mut win_size = unsafe { std::mem::zeroed::<SIZE>() };
+        for mut line in text.lines() {
+            if line.is_empty() {
+                line = " ";
+            }
+            let text = WideString::new(line);
+            let mut text = text.as_slice();
+            let mut extents = vec![0i32; text.len()];
+            while !text.is_empty() {
+                unsafe {
+                    Gdi::GetTextExtentExPointW(
+                        hdc,
+                        text.as_ptr(),
+                        text.len() as i32,
+                        size.width.try_into().unwrap(),
+                        &mut char_fit,
+                        extents.as_mut_ptr(),
+                        &mut win_size,
+                    );
+                }
+                if char_fit == 0 {
+                    return;
+                }
+                let mut split = char_fit as usize;
+                let mut split_end = split.saturating_sub(1);
+                if (char_fit as usize) < text.len() {
+                    for i in (0..char_fit as usize).rev() {
+                        // FIXME safer utf16 handling?
+                        if text[i] == b' ' as u16 {
+                            split = i + 1;
+                            split_end = i.saturating_sub(1);
+                            break;
+                        }
+                    }
+                }
+                text = &text[split..];
+                max_width = std::cmp::max(max_width, extents[split_end].try_into().unwrap());
+                let measured_height: u32 = win_size.cy.try_into().unwrap();
+                height += measured_height;
+            }
+        }
+        unsafe { Gdi::ReleaseDC(window, hdc) };
+
+        assert!(max_width <= size.width);
+        size.width = max_width;
+        size.height = height;
+    }
+}
+
+#[derive(Debug, Default, Clone, Copy)]
+struct Size {
+    pub width: u32,
+    pub height: u32,
+}
+
+impl Size {
+    pub fn inner_size(&self, style: &ElementStyle) -> Self {
+        let mut ret = self.less_margin(&style.margin);
+        if let Some(width) = style.horizontal_size_request {
+            ret.width = width;
+        }
+        if let Some(height) = style.vertical_size_request {
+            ret.height = height;
+        }
+        ret
+    }
+
+    pub fn from_content_size(&mut self, style: &ElementStyle, content_size: &Self) {
+        if style.horizontal_size_request.is_none() && style.horizontal_alignment != Alignment::Fill
+        {
+            self.width = content_size.width;
+        }
+        if style.vertical_size_request.is_none() && style.vertical_alignment != Alignment::Fill {
+            self.height = content_size.height;
+        }
+    }
+
+    pub fn plus_margin(&self, margin: &Margin) -> Self {
+        let mut ret = self.clone();
+        ret.width += margin.start + margin.end;
+        ret.height += margin.top + margin.bottom;
+        ret
+    }
+
+    pub fn less_margin(&self, margin: &Margin) -> Self {
+        let mut ret = self.clone();
+        ret.width = ret.width.saturating_sub(margin.start + margin.end);
+        ret.height = ret.height.saturating_sub(margin.top + margin.bottom);
+        ret
+    }
+}
+
+#[derive(Debug, Default, Clone, Copy)]
+struct Position {
+    pub start: u32,
+    pub top: u32,
+}
+
+impl Position {
+    #[allow(dead_code)]
+    pub fn plus_margin(&self, margin: &Margin) -> Self {
+        let mut ret = self.clone();
+        ret.start = ret.start.saturating_sub(margin.start);
+        ret.top = ret.top.saturating_sub(margin.top);
+        ret
+    }
+
+    pub fn less_margin(&self, margin: &Margin) -> Self {
+        let mut ret = self.clone();
+        ret.start += margin.start;
+        ret.top += margin.top;
+        ret
+    }
+}
+
+fn is_visible(style: &ElementStyle) -> bool {
+    match &style.visible {
+        Property::Static(v) => *v,
+        Property::Binding(s) => *s.borrow(),
+        _ => true,
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/ui/windows/mod.rs b/toolkit/crashreporter/client/app/src/ui/windows/mod.rs
new file mode 100644
index 0000000000..c2f396b80d
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/ui/windows/mod.rs
@@ -0,0 +1,949 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! A UI using the windows API.
+//!
+//! This UI contains some edge cases that aren't implemented, for instance:
+//! * there are a few cases where specific hierarchies are handled differently (e.g. a Button
+//!   containing Label, Scroll behavior, etc).
+//! * not all controls handle all Property variants (e.g. Checkbox doesn't handle ReadOnly, TextBox
+//!   doesn't handle Binding, etc).
+//!
+//! The error handling is also a _little_ fast-and-loose, as many functions return an error value
+//! that is acceptable to following logic (though it still would be a good idea to improve this).
+//!
+//! The rendering treats VBox, HBox, and Scroll as strictly layout-only: they do not create any
+//! associated windows, and the layout logic handles their behavior.
+
+// Our windows-targets doesn't link uxtheme correctly for GetThemeSysFont/GetThemeSysColor.
+// This was working in windows-sys 0.48.
+#[link(name = "uxtheme", kind = "static")]
+extern "C" {}
+
+use super::model::{self, Application, Element, ElementStyle, TypedElement};
+use crate::data::Property;
+use font::Font;
+use once_cell::sync::Lazy;
+use quit_token::QuitToken;
+use std::cell::RefCell;
+use std::collections::HashMap;
+use std::pin::Pin;
+use std::rc::Rc;
+use widestring::WideString;
+use window::{CustomWindowClass, Window, WindowBuilder};
+use windows_sys::Win32::{
+    Foundation::{HINSTANCE, HWND, LPARAM, LRESULT, RECT, WPARAM},
+    Graphics::Gdi,
+    System::{LibraryLoader::GetModuleHandleW, SystemServices, Threading::GetCurrentThreadId},
+    UI::{Controls, Input::KeyboardAndMouse, Shell, WindowsAndMessaging as win},
+};
+
+macro_rules! success {
+    ( nonzero $e:expr ) => {{
+        let value = $e;
+        assert_ne!(value, 0);
+        value
+    }};
+    ( lasterror $e:expr ) => {{
+        unsafe { windows_sys::Win32::Foundation::SetLastError(0) };
+        let value = $e;
+        assert!(value != 0 || windows_sys::Win32::Foundation::GetLastError() == 0);
+        value
+    }};
+    ( hresult $e:expr ) => {
+        assert_eq!($e, windows_sys::Win32::Foundation::S_OK);
+    };
+    ( pointer $e:expr ) => {{
+        let ptr = $e;
+        assert_ne!(ptr, 0);
+        ptr
+    }};
+}
+
+mod font;
+mod gdi;
+mod layout;
+mod quit_token;
+mod twoway;
+mod widestring;
+mod window;
+
+/// A Windows API UI implementation.
+pub struct UI {
+    thread_id: u32,
+}
+
+/// Custom user messages.
+#[repr(u32)]
+enum UserMessage {
+    Invoke = win::WM_USER,
+}
+
+fn get_invoke(msg: &win::MSG) -> Option<Box<model::InvokeFn>> {
+    if msg.message == UserMessage::Invoke as u32 {
+        Some(unsafe { Box::from_raw(msg.lParam as *mut model::InvokeFn) })
+    } else {
+        None
+    }
+}
+
+impl UI {
+    pub fn run_loop(&self, app: Application) {
+        // Initialize common controls.
+        {
+            let icc = Controls::INITCOMMONCONTROLSEX {
+                dwSize: std::mem::size_of::<Controls::INITCOMMONCONTROLSEX>() as _,
+                // Buttons, edit controls, and static controls are all included in 'standard'.
+                dwICC: Controls::ICC_STANDARD_CLASSES | Controls::ICC_PROGRESS_CLASS,
+            };
+            success!(nonzero unsafe { Controls::InitCommonControlsEx(&icc) });
+        }
+
+        // Enable font smoothing (per
+        // https://learn.microsoft.com/en-us/windows/win32/gdi/cleartype-antialiasing ).
+        unsafe {
+            // We don't check for failure on these, they are best-effort.
+            win::SystemParametersInfoW(
+                win::SPI_SETFONTSMOOTHING,
+                1,
+                std::ptr::null_mut(),
+                win::SPIF_UPDATEINIFILE | win::SPIF_SENDCHANGE,
+            );
+            win::SystemParametersInfoW(
+                win::SPI_SETFONTSMOOTHINGTYPE,
+                0,
+                win::FE_FONTSMOOTHINGCLEARTYPE as _,
+                win::SPIF_UPDATEINIFILE | win::SPIF_SENDCHANGE,
+            );
+        }
+
+        // Enable correct layout direction.
+        if unsafe { win::SetProcessDefaultLayout(if app.rtl { Gdi::LAYOUT_RTL } else { 0 }) } == 0 {
+            log::warn!("failed to set process layout direction");
+        }
+
+        let module: HINSTANCE = unsafe { GetModuleHandleW(std::ptr::null()) };
+
+        // Register custom classes.
+        AppWindow::register(module).expect("failed to register AppWindow window class");
+
+        {
+            // The quit token is cloned for each top-level window and dropped at the end of this
+            // scope.
+            let quit_token = QuitToken::new();
+
+            for window in app.windows {
+                let name = WideString::new(window.element_type.title.as_str());
+                let w = top_level_window(
+                    module,
+                    AppWindow::new(
+                        WindowRenderer::new(module, window.element_type, &window.style),
+                        Some(quit_token.clone()),
+                    ),
+                    &name,
+                    &window.style,
+                );
+
+                unsafe { win::ShowWindow(w.handle, win::SW_NORMAL) };
+                unsafe { Gdi::UpdateWindow(w.handle) };
+            }
+        }
+
+        // Run the event loop.
+        let mut msg = unsafe { std::mem::zeroed::<win::MSG>() };
+        while unsafe { win::GetMessageW(&mut msg, 0, 0, 0) } > 0 {
+            if let Some(f) = get_invoke(&msg) {
+                f();
+                continue;
+            }
+
+            unsafe {
+                // IsDialogMessageW is necessary to handle niceties like tab navigation
+                if win::IsDialogMessageW(win::GetAncestor(msg.hwnd, win::GA_ROOT), &mut msg) == 0 {
+                    win::TranslateMessage(&msg);
+                    win::DispatchMessageW(&msg);
+                }
+            }
+        }
+
+        // Flush queue to properly drop late invokes (this is a very unlikely case)
+        while unsafe { win::PeekMessageW(&mut msg, 0, 0, 0, win::PM_REMOVE) } > 0 {
+            if let Some(f) = get_invoke(&msg) {
+                drop(f);
+            }
+        }
+    }
+
+    pub fn invoke(&self, f: model::InvokeFn) {
+        let ptr: *mut model::InvokeFn = Box::into_raw(Box::new(f));
+        if unsafe {
+            win::PostThreadMessageW(self.thread_id, UserMessage::Invoke as u32, 0, ptr as _)
+        } == 0
+        {
+            let _ = unsafe { Box::from_raw(ptr) };
+            log::warn!("failed to invoke function on thread message queue");
+        }
+    }
+}
+
+impl Default for UI {
+    fn default() -> Self {
+        UI {
+            thread_id: unsafe { GetCurrentThreadId() },
+        }
+    }
+}
+
+/// A reference to an Element.
+#[derive(PartialEq, Eq, Hash, Clone, Copy)]
+struct ElementRef(*const Element);
+
+impl ElementRef {
+    pub fn new(element: &Element) -> Self {
+        ElementRef(element as *const Element)
+    }
+
+    /// # Safety
+    /// You must ensure the reference is still valid.
+    pub unsafe fn get(&self) -> &Element {
+        &*self.0
+    }
+}
+
+// Equivalent of win32 HIWORD macro
+fn hiword(v: u32) -> u16 {
+    (v >> 16) as u16
+}
+
+// Equivalent of win32 LOWORD macro
+fn loword(v: u32) -> u16 {
+    v as u16
+}
+
+// Equivalent of win32 MAKELONG macro
+fn makelong(low: u16, high: u16) -> u32 {
+    (high as u32) << 16 | low as u32
+}
+
+fn top_level_window<W: window::WindowClass + window::WindowData>(
+    module: HINSTANCE,
+    class: W,
+    title: &WideString,
+    style: &ElementStyle,
+) -> Window<W> {
+    class
+        .builder(module)
+        .name(title)
+        .style(win::WS_OVERLAPPEDWINDOW)
+        .pos(win::CW_USEDEFAULT, win::CW_USEDEFAULT)
+        .size(
+            style
+                .horizontal_size_request
+                .and_then(|i| i.try_into().ok())
+                .unwrap_or(win::CW_USEDEFAULT),
+            style
+                .vertical_size_request
+                .and_then(|i| i.try_into().ok())
+                .unwrap_or(win::CW_USEDEFAULT),
+        )
+        .create()
+}
+
+window::basic_window_classes! {
+    /// Static control (text, image, etc) class.
+    struct Static => "STATIC";
+
+    /// Button control class.
+    struct Button => "BUTTON";
+
+    /// Edit control class.
+    struct Edit => "EDIT";
+
+    /// Progress control class.
+    struct Progress => "msctls_progress32";
+}
+
+/// A top-level application window.
+///
+/// This is used for the main window and modal windows.
+struct AppWindow {
+    renderer: WindowRenderer,
+    _quit_token: Option<QuitToken>,
+}
+
+impl AppWindow {
+    pub fn new(renderer: WindowRenderer, quit_token: Option<QuitToken>) -> Self {
+        AppWindow {
+            renderer,
+            _quit_token: quit_token,
+        }
+    }
+}
+
+impl window::WindowClass for AppWindow {
+    fn class_name() -> WideString {
+        WideString::new("App Window")
+    }
+}
+
+impl CustomWindowClass for AppWindow {
+    fn icon() -> win::HICON {
+        static ICON: Lazy<win::HICON> = Lazy::new(|| unsafe {
+            // If CreateIconFromResource fails it returns NULL, which is fine (a default icon will be
+            // used).
+            win::CreateIconFromResource(
+                // We take advantage of the fact that since Windows Vista, an RT_ICON resource entry
+                // can simply be a PNG image.
+                super::icon::PNG_DATA.as_ptr(),
+                super::icon::PNG_DATA.len() as u32,
+                true.into(),
+                // The 0x00030000 constant isn't available anywhere; the docs basically say to just
+                // pass it...
+                0x00030000,
+            )
+        });
+
+        *ICON
+    }
+
+    fn message(
+        data: &RefCell<Self>,
+        hwnd: HWND,
+        umsg: u32,
+        wparam: WPARAM,
+        lparam: LPARAM,
+    ) -> Option<LRESULT> {
+        let me = data.borrow();
+        let model = me.renderer.model();
+        match umsg {
+            win::WM_CREATE => {
+                if let Some(close) = &model.close {
+                    close.subscribe(move |&()| unsafe {
+                        win::SendMessageW(hwnd, win::WM_CLOSE, 0, 0);
+                    });
+                }
+
+                let mut renderer = me.renderer.child_renderer(hwnd);
+                if let Some(child) = &model.content {
+                    renderer.render_child(child);
+                }
+
+                drop(model);
+                let children = std::mem::take(&mut me.renderer.model_mut().children);
+                for child in children {
+                    renderer.render_window(child);
+                }
+            }
+            win::WM_CLOSE => {
+                if model.modal {
+                    // Modal windows should hide themselves rather than closing/destroying.
+                    unsafe { win::ShowWindow(hwnd, win::SW_HIDE) };
+                    return Some(0);
+                }
+            }
+            win::WM_SHOWWINDOW => {
+                if model.modal {
+                    // Modal windows should disable/enable their parent as they are shown/hid,
+                    // respectively.
+                    let shown = wparam != 0;
+                    unsafe {
+                        KeyboardAndMouse::EnableWindow(
+                            win::GetWindow(hwnd, win::GW_OWNER),
+                            (!shown).into(),
+                        )
+                    };
+                    return Some(0);
+                }
+            }
+            win::WM_GETMINMAXINFO => {
+                let minmaxinfo = unsafe { (lparam as *mut win::MINMAXINFO).as_mut().unwrap() };
+                minmaxinfo.ptMinTrackSize.x = me.renderer.min_size.0.try_into().unwrap();
+                minmaxinfo.ptMinTrackSize.y = me.renderer.min_size.1.try_into().unwrap();
+                return Some(0);
+            }
+            win::WM_SIZE => {
+                // When resized, recompute the layout.
+                let width = loword(lparam as _) as u32;
+                let height = hiword(lparam as _) as u32;
+
+                if let Some(child) = &model.content {
+                    me.renderer.layout(child, width, height);
+                    unsafe { Gdi::UpdateWindow(hwnd) };
+                }
+                return Some(0);
+            }
+            win::WM_GETFONT => return Some(**me.renderer.font() as _),
+            win::WM_COMMAND => {
+                let child = lparam as HWND;
+                let windows = me.renderer.windows.borrow();
+                if let Some(&element) = windows.reverse().get(&child) {
+                    // # Safety
+                    // The ElementRefs all pertain to the model stored in the renderer.
+                    let element = unsafe { element.get() };
+                    // Handle button presses.
+                    use model::ElementType::*;
+                    match &element.element_type {
+                        Button(model::Button { click, .. }) => {
+                            let code = hiword(wparam as _) as u32;
+                            if code == win::BN_CLICKED {
+                                click.fire(&());
+                                return Some(0);
+                            }
+                        }
+                        Checkbox(model::Checkbox { checked, .. }) => {
+                            let code = hiword(wparam as _) as u32;
+                            if code == win::BN_CLICKED {
+                                let check_state =
+                                    unsafe { win::SendMessageW(child, win::BM_GETCHECK, 0, 0) };
+                                if let Property::Binding(s) = checked {
+                                    *s.borrow_mut() = check_state == Controls::BST_CHECKED as isize;
+                                }
+                                return Some(0);
+                            }
+                        }
+                        _ => (),
+                    }
+                }
+            }
+            _ => (),
+        }
+        None
+    }
+}
+
+/// State used while creating and updating windows.
+struct WindowRenderer {
+    // We wrap with an Rc to get weak references in property callbacks (like that of
+    // `ElementStyle::visible`).
+    inner: Rc<WindowRendererInner>,
+}
+
+impl std::ops::Deref for WindowRenderer {
+    type Target = WindowRendererInner;
+
+    fn deref(&self) -> &Self::Target {
+        &self.inner
+    }
+}
+
+struct WindowRendererInner {
+    pub module: HINSTANCE,
+    /// The model is pinned and boxed to ensure that references in `windows` remain valid.
+    ///
+    /// We need to keep the model around so we can correctly perform layout as the window size
+    /// changes. Unfortunately the win32 API doesn't have any nice ways to automatically perform
+    /// layout.
+    pub model: RefCell<Pin<Box<model::Window>>>,
+    pub min_size: (u32, u32),
+    /// Mapping between model elements and windows.
+    ///
+    /// Element references pertain to elements in `model`.
+    pub windows: RefCell<twoway::TwoWay<ElementRef, HWND>>,
+    pub font: Font,
+    pub bold_font: Font,
+}
+
+impl WindowRenderer {
+    pub fn new(module: HINSTANCE, model: model::Window, style: &model::ElementStyle) -> Self {
+        WindowRenderer {
+            inner: Rc::new(WindowRendererInner {
+                module,
+                model: RefCell::new(Box::pin(model)),
+                min_size: (
+                    style.horizontal_size_request.unwrap_or(0),
+                    style.vertical_size_request.unwrap_or(0),
+                ),
+                windows: Default::default(),
+                font: Font::caption(),
+                bold_font: Font::caption_bold().unwrap_or_else(Font::caption),
+            }),
+        }
+    }
+
+    pub fn child_renderer(&self, window: HWND) -> WindowChildRenderer {
+        WindowChildRenderer {
+            renderer: &self.inner,
+            window,
+            child_id: 0,
+            scroll: false,
+        }
+    }
+
+    pub fn layout(&self, element: &Element, max_width: u32, max_height: u32) {
+        layout::Layout::new(self.inner.windows.borrow().forward())
+            .layout(element, max_width, max_height);
+    }
+
+    pub fn model(&self) -> std::cell::Ref<'_, model::Window> {
+        std::cell::Ref::map(self.inner.model.borrow(), |b| &**b)
+    }
+
+    pub fn model_mut(&self) -> std::cell::RefMut<'_, model::Window> {
+        std::cell::RefMut::map(self.inner.model.borrow_mut(), |b| &mut **b)
+    }
+
+    pub fn font(&self) -> &Font {
+        &self.inner.font
+    }
+}
+
+struct WindowChildRenderer<'a> {
+    renderer: &'a Rc<WindowRendererInner>,
+    window: HWND,
+    child_id: i32,
+    scroll: bool,
+}
+
+impl<'a> WindowChildRenderer<'a> {
+    fn add_child<W: window::WindowClass>(&mut self, class: W) -> WindowBuilder<W> {
+        let builder = class
+            .builder(self.renderer.module)
+            .style(win::WS_CHILD | win::WS_VISIBLE)
+            .parent(self.window)
+            .child_id(self.child_id);
+        self.child_id += 1;
+        builder
+    }
+
+    fn add_window<W: window::WindowClass>(&mut self, class: W) -> WindowBuilder<W> {
+        class
+            .builder(self.renderer.module)
+            .style(win::WS_OVERLAPPEDWINDOW)
+            .pos(win::CW_USEDEFAULT, win::CW_USEDEFAULT)
+            .parent(self.window)
+    }
+
+    fn render_window(&mut self, model: TypedElement<model::Window>) -> Window {
+        let name = WideString::new(model.element_type.title.as_str());
+        let style = model.style;
+        let w = self
+            .add_window(AppWindow::new(
+                WindowRenderer::new(self.renderer.module, model.element_type, &style),
+                None,
+            ))
+            .size(
+                style
+                    .horizontal_size_request
+                    .and_then(|i| i.try_into().ok())
+                    .unwrap_or(win::CW_USEDEFAULT),
+                style
+                    .vertical_size_request
+                    .and_then(|i| i.try_into().ok())
+                    .unwrap_or(win::CW_USEDEFAULT),
+            )
+            .name(&name)
+            .create();
+
+        enabled_property(&style.enabled, w.handle);
+
+        let hwnd = w.handle;
+        let set_visible = move |visible| unsafe {
+            win::ShowWindow(hwnd, if visible { win::SW_SHOW } else { win::SW_HIDE });
+        };
+
+        match &style.visible {
+            Property::Static(false) => set_visible(false),
+            Property::Binding(s) => {
+                s.on_change(move |v| set_visible(*v));
+                if !*s.borrow() {
+                    set_visible(false);
+                }
+            }
+            _ => (),
+        }
+
+        w.generic()
+    }
+
+    fn render_child(&mut self, element: &Element) {
+        if let Some(mut window) = self.render_element_type(&element.element_type) {
+            window.set_default_font(&self.renderer.font);
+
+            // Store the element to handle mapping.
+            self.renderer
+                .windows
+                .borrow_mut()
+                .insert(ElementRef::new(element), window.handle);
+
+            enabled_property(&element.style.enabled, window.handle);
+        }
+
+        // Handle visibility properties.
+        match &element.style.visible {
+            Property::Static(false) => {
+                set_visibility(element, false, self.renderer.windows.borrow().forward())
+            }
+            Property::Binding(s) => {
+                let weak_renderer = Rc::downgrade(self.renderer);
+                let element_ref = ElementRef::new(element);
+                let parent = self.window;
+                s.on_change(move |visible| {
+                    let Some(renderer) = weak_renderer.upgrade() else {
+                        return;
+                    };
+                    // # Safety
+                    // ElementRefs are valid as long as the renderer is (and we have a strong
+                    // reference to it).
+                    let element = unsafe { element_ref.get() };
+                    set_visibility(element, *visible, renderer.windows.borrow().forward());
+                    // Send WM_SIZE so that the parent recomputes the layout.
+                    unsafe {
+                        let mut rect = std::mem::zeroed::<RECT>();
+                        win::GetClientRect(parent, &mut rect);
+                        win::SendMessageW(
+                            parent,
+                            win::WM_SIZE,
+                            0,
+                            makelong(
+                                (rect.right - rect.left) as u16,
+                                (rect.bottom - rect.top) as u16,
+                            ) as isize,
+                        );
+                    }
+                });
+                if !*s.borrow() {
+                    set_visibility(element, false, self.renderer.windows.borrow().forward());
+                }
+            }
+            _ => (),
+        }
+    }
+
+    fn render_element_type(&mut self, element_type: &model::ElementType) -> Option<Window> {
+        use model::ElementType as ET;
+        match element_type {
+            ET::Label(model::Label { text, bold }) => {
+                let mut window = match text {
+                    Property::Static(text) => {
+                        let text = WideString::new(text.as_str());
+                        self.add_child(Static)
+                            .name(&text)
+                            .add_style(SystemServices::SS_LEFT | SystemServices::SS_NOPREFIX)
+                            .create()
+                    }
+                    Property::Binding(b) => {
+                        let text = WideString::new(b.borrow().as_str());
+                        let window = self
+                            .add_child(Static)
+                            .name(&text)
+                            .add_style(SystemServices::SS_LEFT | SystemServices::SS_NOPREFIX)
+                            .create();
+                        let handle = window.handle;
+                        b.on_change(move |text| {
+                            let text = WideString::new(text.as_str());
+                            unsafe { win::SetWindowTextW(handle, text.pcwstr()) };
+                        });
+                        window
+                    }
+                    Property::ReadOnly(_) => {
+                        unimplemented!("ReadOnly property not supported for Label::text")
+                    }
+                };
+                if *bold {
+                    window.set_font(&self.renderer.bold_font);
+                }
+                Some(window.generic())
+            }
+            ET::TextBox(model::TextBox {
+                placeholder,
+                content,
+                editable,
+            }) => {
+                let scroll = self.scroll;
+                let window = self
+                    .add_child(Edit)
+                    .add_style(
+                        (win::ES_LEFT
+                            | win::ES_MULTILINE
+                            | win::ES_WANTRETURN
+                            | if *editable { 0 } else { win::ES_READONLY })
+                            as u32
+                            | win::WS_BORDER
+                            | win::WS_TABSTOP
+                            | if scroll { win::WS_VSCROLL } else { 0 },
+                    )
+                    .create();
+
+                fn to_control_text(s: &str) -> String {
+                    s.replace("\n", "\r\n")
+                }
+
+                fn from_control_text(s: &str) -> String {
+                    s.replace("\r\n", "\n")
+                }
+
+                struct SubClassData {
+                    placeholder: Option<WideString>,
+                }
+
+                // EM_SETCUEBANNER doesn't work with multiline edit controls (for no particular
+                // reason?), so we have to draw it ourselves.
+                unsafe extern "system" fn subclass_proc(
+                    hwnd: HWND,
+                    msg: u32,
+                    wparam: WPARAM,
+                    lparam: LPARAM,
+                    _uidsubclass: usize,
+                    dw_ref_data: usize,
+                ) -> LRESULT {
+                    let ret = Shell::DefSubclassProc(hwnd, msg, wparam, lparam);
+                    if msg == win::WM_PAINT
+                        && KeyboardAndMouse::GetFocus() != hwnd
+                        && win::GetWindowTextLengthW(hwnd) == 0
+                    {
+                        let data = (dw_ref_data as *const SubClassData).as_ref().unwrap();
+                        if let Some(placeholder) = &data.placeholder {
+                            let mut rect = std::mem::zeroed::<RECT>();
+                            win::GetClientRect(hwnd, &mut rect);
+                            Gdi::InflateRect(&mut rect, -2, -2);
+
+                            let dc = gdi::DC::new(hwnd).expect("failed to create GDI DC");
+                            dc.with_object_selected(
+                                win::SendMessageW(hwnd, win::WM_GETFONT, 0, 0) as _,
+                                |hdc| {
+                                    Gdi::SetTextColor(
+                                        hdc,
+                                        Controls::GetThemeSysColor(0, Gdi::COLOR_GRAYTEXT),
+                                    );
+                                    Gdi::SetBkMode(hdc, Gdi::TRANSPARENT as i32);
+                                    success!(nonzero Gdi::DrawTextW(
+                                        hdc,
+                                        placeholder.pcwstr(),
+                                        -1,
+                                        &mut rect,
+                                        Gdi::DT_LEFT | Gdi::DT_TOP | Gdi::DT_WORDBREAK,
+                                    ));
+                                },
+                            )
+                            .expect("failed to select font gdi object");
+                        }
+                    }
+
+                    // Multiline edit controls capture the tab key. We want it to work as usual in
+                    // the dialog (focusing the next input control).
+                    if msg == win::WM_GETDLGCODE && wparam == KeyboardAndMouse::VK_TAB as usize {
+                        return 0;
+                    }
+
+                    if msg == win::WM_DESTROY {
+                        drop(unsafe { Box::from_raw(dw_ref_data as *mut SubClassData) });
+                    }
+                    return ret;
+                }
+
+                let subclassdata = Box::into_raw(Box::new(SubClassData {
+                    placeholder: placeholder
+                        .as_ref()
+                        .map(|s| WideString::new(to_control_text(s))),
+                }));
+
+                unsafe {
+                    Shell::SetWindowSubclass(
+                        window.handle,
+                        Some(subclass_proc),
+                        0,
+                        subclassdata as _,
+                    );
+                }
+
+                // Set up content property.
+                match content {
+                    Property::ReadOnly(od) => {
+                        let handle = window.handle;
+                        od.register(move |target| {
+                            // GetWindowText requires the buffer be large enough for the terminating
+                            // null character (otherwise it truncates the string), but
+                            // GetWindowTextLength returns the length without the null character, so we
+                            // add 1.
+                            let length = unsafe { win::GetWindowTextLengthW(handle) } + 1;
+                            let mut buf = vec![0u16; length as usize];
+                            unsafe { win::GetWindowTextW(handle, buf.as_mut_ptr(), length) };
+                            buf.pop(); // null character; `String` doesn't want that
+                            *target = from_control_text(&String::from_utf16_lossy(&buf));
+                        });
+                    }
+                    Property::Static(s) => {
+                        let text = WideString::new(to_control_text(s));
+                        unsafe { win::SetWindowTextW(window.handle, text.pcwstr()) };
+                    }
+                    Property::Binding(b) => {
+                        let handle = window.handle;
+                        b.on_change(move |text| {
+                            let text = WideString::new(to_control_text(text.as_str()));
+                            unsafe { win::SetWindowTextW(handle, text.pcwstr()) };
+                        });
+                        let text = WideString::new(to_control_text(b.borrow().as_str()));
+                        unsafe { win::SetWindowTextW(window.handle, text.pcwstr()) };
+                    }
+                }
+                Some(window.generic())
+            }
+            ET::Scroll(model::Scroll { content }) => {
+                if let Some(content) = content {
+                    // Scrolling is implemented in a cooperative, non-universal way right now.
+                    self.scroll = true;
+                    self.render_child(content);
+                    self.scroll = false;
+                }
+                None
+            }
+            ET::Button(model::Button { content, .. }) => {
+                if let Some(ET::Label(model::Label {
+                    text: Property::Static(text),
+                    ..
+                })) = content.as_ref().map(|e| &e.element_type)
+                {
+                    let text = WideString::new(text);
+
+                    let window = self
+                        .add_child(Button)
+                        .add_style(win::BS_PUSHBUTTON as u32 | win::WS_TABSTOP)
+                        .name(&text)
+                        .create();
+                    Some(window.generic())
+                } else {
+                    None
+                }
+            }
+            ET::Checkbox(model::Checkbox { checked, label }) => {
+                let label = label.as_ref().map(WideString::new);
+                let mut builder = self
+                    .add_child(Button)
+                    .add_style((win::BS_AUTOCHECKBOX | win::BS_MULTILINE) as u32 | win::WS_TABSTOP);
+                if let Some(label) = &label {
+                    builder = builder.name(label);
+                }
+                let window = builder.create();
+
+                fn set_check(handle: HWND, value: bool) {
+                    unsafe {
+                        win::SendMessageW(
+                            handle,
+                            win::BM_SETCHECK,
+                            if value {
+                                Controls::BST_CHECKED
+                            } else {
+                                Controls::BST_UNCHECKED
+                            } as usize,
+                            0,
+                        );
+                    }
+                }
+
+                match checked {
+                    Property::Static(checked) => set_check(window.handle, *checked),
+                    Property::Binding(s) => {
+                        let handle = window.handle;
+                        s.on_change(move |v| {
+                            set_check(handle, *v);
+                        });
+                        set_check(window.handle, *s.borrow());
+                    }
+                    _ => unimplemented!("ReadOnly properties not supported for Checkbox"),
+                }
+
+                Some(window.generic())
+            }
+            ET::Progress(model::Progress { amount }) => {
+                let window = self
+                    .add_child(Progress)
+                    .add_style(Controls::PBS_MARQUEE)
+                    .create();
+
+                fn set_amount(handle: HWND, value: Option<f32>) {
+                    match value {
+                        None => unsafe {
+                            win::SendMessageW(handle, Controls::PBM_SETMARQUEE, 1, 0);
+                        },
+                        Some(v) => unsafe {
+                            win::SendMessageW(handle, Controls::PBM_SETMARQUEE, 0, 0);
+                            win::SendMessageW(
+                                handle,
+                                Controls::PBM_SETPOS,
+                                (v.clamp(0f32, 1f32) * 100f32) as usize,
+                                0,
+                            );
+                        },
+                    }
+                }
+
+                match amount {
+                    Property::Static(v) => set_amount(window.handle, *v),
+                    Property::Binding(s) => {
+                        let handle = window.handle;
+                        s.on_change(move |v| set_amount(handle, *v));
+                        set_amount(window.handle, *s.borrow());
+                    }
+                    _ => unimplemented!("ReadOnly properties not supported for Progress"),
+                }
+
+                Some(window.generic())
+            }
+            // VBox/HBox are virtual, their behaviors are implemented entirely in the renderer layout.
+            // No need for additional windows.
+            ET::VBox(model::VBox { items, .. }) => {
+                for item in items {
+                    self.render_child(item);
+                }
+                None
+            }
+            ET::HBox(model::HBox { items, .. }) => {
+                for item in items {
+                    self.render_child(item);
+                }
+                None
+            }
+        }
+    }
+}
+
+/// Handle the enabled property.
+///
+/// This function assumes the default state of the window is enabled.
+fn enabled_property(enabled: &Property<bool>, window: HWND) {
+    match enabled {
+        Property::Static(false) => unsafe {
+            KeyboardAndMouse::EnableWindow(window, false.into());
+        },
+        Property::Binding(s) => {
+            let handle = window;
+            s.on_change(move |enabled| {
+                unsafe { KeyboardAndMouse::EnableWindow(handle, (*enabled).into()) };
+            });
+            if !*s.borrow() {
+                unsafe { KeyboardAndMouse::EnableWindow(window, false.into()) };
+            }
+        }
+        _ => (),
+    }
+}
+
+/// Set the visibility of the given element. This recurses down the element tree and hides children
+/// as necessary.
+fn set_visibility(element: &Element, visible: bool, windows: &HashMap<ElementRef, HWND>) {
+    if let Some(&hwnd) = windows.get(&ElementRef::new(element)) {
+        unsafe {
+            win::ShowWindow(hwnd, if visible { win::SW_SHOW } else { win::SW_HIDE });
+        }
+    } else {
+        match &element.element_type {
+            model::ElementType::VBox(model::VBox { items, .. }) => {
+                for item in items {
+                    set_visibility(item, visible, windows);
+                }
+            }
+            model::ElementType::HBox(model::HBox { items, .. }) => {
+                for item in items {
+                    set_visibility(item, visible, windows);
+                }
+            }
+            model::ElementType::Scroll(model::Scroll {
+                content: Some(content),
+            }) => {
+                set_visibility(&*content, visible, windows);
+            }
+            _ => (),
+        }
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/ui/windows/quit_token.rs b/toolkit/crashreporter/client/app/src/ui/windows/quit_token.rs
new file mode 100644
index 0000000000..f952db3db4
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/ui/windows/quit_token.rs
@@ -0,0 +1,33 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use std::rc::Rc;
+use windows_sys::Win32::UI::WindowsAndMessaging::PostQuitMessage;
+
+/// A Cloneable token which will post a quit message (with code 0) to the main loop when the last
+/// instance is dropped.
+#[derive(Clone, Default)]
+pub struct QuitToken(#[allow(dead_code)] Rc<QuitTokenInternal>);
+
+impl QuitToken {
+    pub fn new() -> Self {
+        Self::default()
+    }
+}
+
+impl std::fmt::Debug for QuitToken {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        f.debug_struct(std::any::type_name::<Self>())
+            .finish_non_exhaustive()
+    }
+}
+
+#[derive(Default)]
+struct QuitTokenInternal;
+
+impl Drop for QuitTokenInternal {
+    fn drop(&mut self) {
+        unsafe { PostQuitMessage(0) };
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/ui/windows/twoway.rs b/toolkit/crashreporter/client/app/src/ui/windows/twoway.rs
new file mode 100644
index 0000000000..8a18162e08
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/ui/windows/twoway.rs
@@ -0,0 +1,36 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use std::collections::HashMap;
+
+/// A two-way hashmap.
+#[derive(Debug)]
+pub struct TwoWay<K, V> {
+    forward: HashMap<K, V>,
+    reverse: HashMap<V, K>,
+}
+
+impl<K, V> Default for TwoWay<K, V> {
+    fn default() -> Self {
+        TwoWay {
+            forward: Default::default(),
+            reverse: Default::default(),
+        }
+    }
+}
+
+impl<K: Eq + std::hash::Hash + Clone, V: Eq + std::hash::Hash + Clone> TwoWay<K, V> {
+    pub fn insert(&mut self, key: K, value: V) {
+        self.forward.insert(key.clone(), value.clone());
+        self.reverse.insert(value, key);
+    }
+
+    pub fn forward(&self) -> &HashMap<K, V> {
+        &self.forward
+    }
+
+    pub fn reverse(&self) -> &HashMap<V, K> {
+        &self.reverse
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/ui/windows/widestring.rs b/toolkit/crashreporter/client/app/src/ui/windows/widestring.rs
new file mode 100644
index 0000000000..0dc713352b
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/ui/windows/widestring.rs
@@ -0,0 +1,36 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use std::ffi::OsStr;
+use std::os::windows::ffi::OsStrExt;
+use windows_sys::core::PCWSTR;
+
+/// Windows wide strings.
+///
+/// These are utf16 encoded with a terminating null character (0).
+pub struct WideString(Vec<u16>);
+
+impl WideString {
+    pub fn new(os_str: impl AsRef<OsStr>) -> Self {
+        // TODO: doesn't check whether the OsStr contains a null character, which could be treated
+        // as an error (as `CString::new` does).
+        WideString(
+            os_str
+                .as_ref()
+                .encode_wide()
+                .chain(std::iter::once(0))
+                // Remove unicode BIDI markers (from fluent) which aren't rendered correctly.
+                .filter(|c| *c != 0x2068 && *c != 0x2069)
+                .collect(),
+        )
+    }
+
+    pub fn pcwstr(&self) -> PCWSTR {
+        self.0.as_ptr()
+    }
+
+    pub fn as_slice(&self) -> &[u16] {
+        &self.0
+    }
+}
diff --git a/toolkit/crashreporter/client/app/src/ui/windows/window.rs b/toolkit/crashreporter/client/app/src/ui/windows/window.rs
new file mode 100644
index 0000000000..7e5e8f3f2a
--- /dev/null
+++ b/toolkit/crashreporter/client/app/src/ui/windows/window.rs
@@ -0,0 +1,302 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Types and helpers relating to windows and window classes.
+
+use super::Font;
+use super::WideString;
+use std::cell::RefCell;
+use windows_sys::Win32::{
+    Foundation::{HINSTANCE, HWND, LPARAM, LRESULT, WPARAM},
+    Graphics::Gdi::{self, HBRUSH},
+    UI::WindowsAndMessaging::{self as win, HCURSOR, HICON},
+};
+
+/// Types representing a window class.
+pub trait WindowClass: Sized + 'static {
+    fn class_name() -> WideString;
+
+    fn builder(self, module: HINSTANCE) -> WindowBuilder<'static, Self> {
+        WindowBuilder {
+            name: None,
+            style: None,
+            x: 0,
+            y: 0,
+            width: 0,
+            height: 0,
+            parent: None,
+            child_id: 0,
+            module,
+            data: self,
+        }
+    }
+}
+
+/// Window classes which have their own message handler.
+///
+/// A type implementing this trait provides its data to a single window.
+///
+/// `register` must be called before use.
+pub trait CustomWindowClass: WindowClass {
+    /// Handle a message.
+    fn message(
+        data: &RefCell<Self>,
+        hwnd: HWND,
+        umsg: u32,
+        wparam: WPARAM,
+        lparam: LPARAM,
+    ) -> Option<LRESULT>;
+
+    /// The class's default background brush.
+    fn background() -> HBRUSH {
+        (Gdi::COLOR_3DFACE + 1) as HBRUSH
+    }
+
+    /// The class's default cursor.
+    fn cursor() -> HCURSOR {
+        unsafe { win::LoadCursorW(0, win::IDC_ARROW) }
+    }
+
+    /// The class's default icon.
+    fn icon() -> HICON {
+        0
+    }
+
+    /// Register the class.
+    fn register(module: HINSTANCE) -> anyhow::Result<()> {
+        unsafe extern "system" fn wnd_proc<W: CustomWindowClass>(
+            hwnd: HWND,
+            umsg: u32,
+            wparam: WPARAM,
+            lparam: LPARAM,
+        ) -> LRESULT {
+            if umsg == win::WM_CREATE {
+                let create_struct = &*(lparam as *const win::CREATESTRUCTW);
+                success!(lasterror win::SetWindowLongPtrW(hwnd, 0, create_struct.lpCreateParams as _));
+                // Changes made with SetWindowLongPtr don't take effect until SetWindowPos is called...
+                success!(nonzero win::SetWindowPos(
+                    hwnd,
+                    win::HWND_TOP,
+                    0,
+                    0,
+                    0,
+                    0,
+                    win::SWP_NOMOVE | win::SWP_NOSIZE | win::SWP_NOZORDER | win::SWP_FRAMECHANGED,
+                ));
+            }
+
+            let result = unsafe { W::get(hwnd).as_ref() }
+                .and_then(|data| W::message(data, hwnd, umsg, wparam, lparam));
+            if umsg == win::WM_DESTROY {
+                drop(Box::from_raw(
+                    win::GetWindowLongPtrW(hwnd, 0) as *mut RefCell<W>
+                ));
+            }
+            result.unwrap_or_else(|| win::DefWindowProcW(hwnd, umsg, wparam, lparam))
+        }
+
+        let class_name = Self::class_name();
+        let window_class = win::WNDCLASSW {
+            lpfnWndProc: Some(wnd_proc::<Self>),
+            hInstance: module,
+            lpszClassName: class_name.pcwstr(),
+            hbrBackground: Self::background(),
+            hIcon: Self::icon(),
+            hCursor: Self::cursor(),
+            cbWndExtra: std::mem::size_of::<isize>() as i32,
+            ..unsafe { std::mem::zeroed() }
+        };
+
+        if unsafe { win::RegisterClassW(&window_class) } == 0 {
+            anyhow::bail!("RegisterClassW failed")
+        }
+        Ok(())
+    }
+
+    /// Get the window data from a window created with this class.
+    ///
+    /// # Safety
+    /// This must only be called on window handles which were created with this class.
+    unsafe fn get(hwnd: HWND) -> *const RefCell<Self> {
+        win::GetWindowLongPtrW(hwnd, 0) as *const RefCell<Self>
+    }
+}
+
+/// Types that can be stored as associated window data.
+pub trait WindowData: Sized {
+    fn to_ptr(self) -> *mut RefCell<Self> {
+        std::ptr::null_mut()
+    }
+}
+
+impl<T: CustomWindowClass> WindowData for T {
+    fn to_ptr(self) -> *mut RefCell<Self> {
+        Box::into_raw(Box::new(RefCell::new(self)))
+    }
+}
+
+macro_rules! basic_window_classes {
+    () => {};
+    ( $(#[$attr:meta])* struct $name:ident => $class:expr; $($rest:tt)* ) => {
+        #[derive(Default)]
+        $(#[$attr])*
+        struct $name;
+
+        impl $crate::ui::ui_impl::window::WindowClass for $name {
+            fn class_name() -> $crate::ui::ui_impl::WideString {
+                $crate::ui::ui_impl::WideString::new($class)
+            }
+        }
+
+        impl $crate::ui::ui_impl::window::WindowData for $name {}
+
+        $crate::ui::ui_impl::window::basic_window_classes!($($rest)*);
+    }
+}
+
+pub(crate) use basic_window_classes;
+
+pub struct WindowBuilder<'a, W> {
+    name: Option<&'a WideString>,
+    style: Option<u32>,
+    x: i32,
+    y: i32,
+    width: i32,
+    height: i32,
+    parent: Option<HWND>,
+    child_id: i32,
+    module: HINSTANCE,
+    data: W,
+}
+
+impl<'a, W> WindowBuilder<'a, W> {
+    #[must_use]
+    pub fn name<'b>(self, s: &'b WideString) -> WindowBuilder<'b, W> {
+        WindowBuilder {
+            name: Some(s),
+            style: self.style,
+            x: self.x,
+            y: self.y,
+            width: self.width,
+            height: self.height,
+            parent: self.parent,
+            child_id: self.child_id,
+            module: self.module,
+            data: self.data,
+        }
+    }
+
+    #[must_use]
+    pub fn style(mut self, d: u32) -> Self {
+        self.style = Some(d);
+        self
+    }
+
+    #[must_use]
+    pub fn add_style(mut self, d: u32) -> Self {
+        *self.style.get_or_insert(0) |= d;
+        self
+    }
+
+    #[must_use]
+    pub fn pos(mut self, x: i32, y: i32) -> Self {
+        self.x = x;
+        self.y = y;
+        self
+    }
+
+    #[must_use]
+    pub fn size(mut self, width: i32, height: i32) -> Self {
+        self.width = width;
+        self.height = height;
+        self
+    }
+
+    #[must_use]
+    pub fn parent(mut self, parent: HWND) -> Self {
+        self.parent = Some(parent);
+        self
+    }
+
+    #[must_use]
+    pub fn child_id(mut self, id: i32) -> Self {
+        self.child_id = id;
+        self
+    }
+
+    pub fn create(self) -> Window<W>
+    where
+        W: WindowClass + WindowData,
+    {
+        let class_name = W::class_name();
+        let handle = unsafe {
+            win::CreateWindowExW(
+                0,
+                class_name.pcwstr(),
+                self.name.map(|n| n.pcwstr()).unwrap_or(std::ptr::null()),
+                self.style.unwrap_or_default(),
+                self.x,
+                self.y,
+                self.width,
+                self.height,
+                self.parent.unwrap_or_default(),
+                self.child_id as _,
+                self.module,
+                self.data.to_ptr() as _,
+            )
+        };
+        assert!(handle != 0);
+
+        Window {
+            handle,
+            child_id: self.child_id,
+            font_set: false,
+            _class: std::marker::PhantomData,
+        }
+    }
+}
+
+/// A window handle with a known class type.
+///
+/// Without a type parameter (defaulting to `()`), the window handle is generic (class type
+/// unknown).
+pub struct Window<W: 'static = ()> {
+    pub handle: HWND,
+    pub child_id: i32,
+    font_set: bool,
+    _class: std::marker::PhantomData<&'static RefCell<W>>,
+}
+
+impl<W: CustomWindowClass> Window<W> {
+    /// Get the window data of the window.
+    #[allow(dead_code)]
+    pub fn data(&self) -> &RefCell<W> {
+        unsafe { W::get(self.handle).as_ref().unwrap() }
+    }
+}
+
+impl<W> Window<W> {
+    /// Get a generic window handle.
+    pub fn generic(self) -> Window {
+        Window {
+            handle: self.handle,
+            child_id: self.child_id,
+            font_set: self.font_set,
+            _class: std::marker::PhantomData,
+        }
+    }
+
+    /// Set a window's font.
+    pub fn set_font(&mut self, font: &Font) {
+        unsafe { win::SendMessageW(self.handle, win::WM_SETFONT, **font as _, 1 as _) };
+        self.font_set = true;
+    }
+
+    /// Set a window's font if not already set.
+    pub fn set_default_font(&mut self, font: &Font) {
+        if !self.font_set {
+            self.set_font(font);
+        }
+    }
+}
diff --git a/toolkit/crashreporter/client/cocoabind/Cargo.toml b/toolkit/crashreporter/client/cocoabind/Cargo.toml
new file mode 100644
index 0000000000..70a0f36582
--- /dev/null
+++ b/toolkit/crashreporter/client/cocoabind/Cargo.toml
@@ -0,0 +1,12 @@
+[package]
+name = "cocoabind"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+block = "0.1"
+objc = "0.2"
+
+[build-dependencies]
+bindgen = { version = "0.69", default-features = false, features = ["runtime"] }
+mozbuild = "0.1.0"
diff --git a/toolkit/crashreporter/client/cocoabind/build.rs b/toolkit/crashreporter/client/cocoabind/build.rs
new file mode 100644
index 0000000000..ba91a87e97
--- /dev/null
+++ b/toolkit/crashreporter/client/cocoabind/build.rs
@@ -0,0 +1,74 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+use mozbuild::config::CC_BASE_FLAGS as CFLAGS;
+
+const TYPES: &[&str] = &[
+    "ActionCell",
+    "Application",
+    "Array",
+    "AttributedString",
+    "Box",
+    "Button",
+    "ButtonCell",
+    "Cell",
+    "ClassDescription",
+    "Control",
+    "DefaultRunLoopMode",
+    "Dictionary",
+    "ForegroundColorAttributeName",
+    "LayoutDimension",
+    "LayoutGuide",
+    "LayoutXAxisAnchor",
+    "LayoutYAxisAnchor",
+    "MutableAttributedString",
+    "MutableParagraphStyle",
+    "MutableString",
+    "ModalPanelRunLoopMode",
+    "Panel",
+    "ProcessInfo",
+    "ProgressIndicator",
+    "Proxy",
+    "RunLoop",
+    "ScrollView",
+    "StackView",
+    "String",
+    "TextField",
+    "TextView",
+    "Value",
+    "View",
+    "Window",
+];
+
+fn main() {
+    let mut builder = bindgen::Builder::default()
+        .header_contents(
+            "cocoa_bindings.h",
+            "#define self self_
+            #import <Cocoa/Cocoa.h>
+            ",
+        )
+        .generate_block(true)
+        .prepend_enum_name(false)
+        .clang_args(CFLAGS)
+        .clang_args(["-x", "objective-c"])
+        .clang_arg("-fblocks")
+        .derive_default(true)
+        .allowlist_item("TransformProcessType");
+    for name in TYPES {
+        // (I|P) covers generated traits (interfaces and protocols). `(_.*)?` covers categories
+        // (which are generated as `CLASS_CATEGORY`).
+        builder = builder.allowlist_item(format!("(I|P)?NS{name}(_.*)?"));
+    }
+    let bindings = builder
+        .generate()
+        .expect("unable to generate cocoa bindings");
+    let out_path = std::path::PathBuf::from(std::env::var("OUT_DIR").unwrap());
+    bindings
+        .write_to_file(out_path.join("cocoa_bindings.rs"))
+        .expect("failed to write cocoa bindings");
+    println!("cargo:rustc-link-lib=framework=AppKit");
+    println!("cargo:rustc-link-lib=framework=Cocoa");
+    println!("cargo:rustc-link-lib=framework=Foundation");
+}
diff --git a/toolkit/crashreporter/client/cocoabind/src/lib.rs b/toolkit/crashreporter/client/cocoabind/src/lib.rs
new file mode 100644
index 0000000000..b7271d9d92
--- /dev/null
+++ b/toolkit/crashreporter/client/cocoabind/src/lib.rs
@@ -0,0 +1,10 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+#![allow(non_upper_case_globals)]
+#![allow(non_camel_case_types)]
+#![allow(non_snake_case)]
+#![allow(unused_imports)]
+
+include!(concat!(env!("OUT_DIR"), "/cocoa_bindings.rs"));
diff --git a/toolkit/crashreporter/client/crashreporter.cpp b/toolkit/crashreporter/client/crashreporter.cpp
deleted file mode 100644
index 2887b16170..0000000000
--- a/toolkit/crashreporter/client/crashreporter.cpp
+++ /dev/null
@@ -1,852 +0,0 @@
-/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-#include "crashreporter.h"
-
-#ifdef _MSC_VER
-// Disable exception handler warnings.
-#  pragma warning(disable : 4530)
-#endif
-
-#include <fstream>
-#include <iomanip>
-#include <sstream>
-#include <memory>
-#include <ctime>
-#include <cstdlib>
-#include <cstring>
-#include <string>
-#include <utility>
-
-#ifdef XP_LINUX
-#  include <dlfcn.h>
-#endif
-
-#include "json/json.h"
-#include "nss.h"
-#include "sechash.h"
-
-using std::ifstream;
-using std::ios;
-using std::istream;
-using std::istringstream;
-using std::ofstream;
-using std::ostream;
-using std::ostringstream;
-using std::string;
-using std::unique_ptr;
-using std::vector;
-
-namespace CrashReporter {
-
-StringTable gStrings;
-Json::Value gData;
-string gSettingsPath;
-string gEventsPath;
-string gPingPath;
-int gArgc;
-char** gArgv;
-bool gAutoSubmit;
-
-enum SubmissionResult { Succeeded, Failed };
-
-static unique_ptr<ofstream> gLogStream(nullptr);
-static string gReporterDumpFile;
-static string gExtraFile;
-static string gMemoryFile;
-
-static const char kExtraDataExtension[] = ".extra";
-static const char kMemoryReportExtension[] = ".memory.json.gz";
-
-void UIError(const string& message) {
-  if (gAutoSubmit) {
-    return;
-  }
-
-  string errorMessage;
-  if (!gStrings[ST_CRASHREPORTERERROR].empty()) {
-    char buf[2048];
-    snprintf(buf, 2048, gStrings[ST_CRASHREPORTERERROR].c_str(),
-             message.c_str());
-    errorMessage = buf;
-  } else {
-    errorMessage = message;
-  }
-
-  UIError_impl(errorMessage);
-}
-
-static string Unescape(const string& str) {
-  string ret;
-  for (string::const_iterator iter = str.begin(); iter != str.end(); iter++) {
-    if (*iter == '\\') {
-      iter++;
-      if (*iter == '\\') {
-        ret.push_back('\\');
-      } else if (*iter == 'n') {
-        ret.push_back('\n');
-      } else if (*iter == 't') {
-        ret.push_back('\t');
-      }
-    } else {
-      ret.push_back(*iter);
-    }
-  }
-
-  return ret;
-}
-
-bool ReadStrings(istream& in, StringTable& strings, bool unescape) {
-  while (!in.eof()) {
-    string line;
-    std::getline(in, line);
-    int sep = line.find('=');
-    if (sep >= 0) {
-      string key, value;
-      key = line.substr(0, sep);
-      value = line.substr(sep + 1);
-      if (unescape) value = Unescape(value);
-      strings[key] = value;
-    }
-  }
-
-  return true;
-}
-
-bool ReadStringsFromFile(const string& path, StringTable& strings,
-                         bool unescape) {
-  ifstream* f = UIOpenRead(path, ios::in);
-  bool success = false;
-  if (f->is_open()) {
-    success = ReadStrings(*f, strings, unescape);
-    f->close();
-  }
-
-  delete f;
-  return success;
-}
-
-static bool ReadExtraFile(const string& aExtraDataPath, Json::Value& aExtra) {
-  bool success = false;
-  ifstream* f = UIOpenRead(aExtraDataPath, ios::in);
-  if (f->is_open()) {
-    Json::CharReaderBuilder builder;
-    success = parseFromStream(builder, *f, &aExtra, nullptr);
-  }
-
-  delete f;
-  return success;
-}
-
-static string Basename(const string& file) {
-  string::size_type slashIndex = file.rfind(UI_DIR_SEPARATOR);
-  if (slashIndex != string::npos) {
-    return file.substr(slashIndex + 1);
-  }
-  return file;
-}
-
-static bool ReadEventFile(const string& aPath, string& aEventVersion,
-                          string& aTime, string& aUuid, Json::Value& aData) {
-  bool res = false;
-  ifstream* f = UIOpenRead(aPath, ios::binary);
-
-  if (f->is_open()) {
-    std::getline(*f, aEventVersion, '\n');
-    res = f->good();
-    std::getline(*f, aTime, '\n');
-    res &= f->good();
-    std::getline(*f, aUuid, '\n');
-    res &= f->good();
-
-    if (res) {
-      Json::CharReaderBuilder builder;
-      res = parseFromStream(builder, *f, &aData, nullptr);
-    }
-  }
-
-  delete f;
-  return res;
-}
-
-static void OverwriteEventFile(const string& aPath, const string& aEventVersion,
-                               const string& aTime, const string& aUuid,
-                               const Json::Value& aData) {
-  ofstream* f = UIOpenWrite(aPath, ios::binary | ios::trunc);
-  if (f->is_open()) {
-    f->write(aEventVersion.c_str(), aEventVersion.length()) << '\n';
-    f->write(aTime.c_str(), aTime.length()) << '\n';
-    f->write(aUuid.c_str(), aUuid.length()) << '\n';
-
-    Json::StreamWriterBuilder builder;
-    builder["indentation"] = "";
-    std::unique_ptr<Json::StreamWriter> writer(builder.newStreamWriter());
-    writer->write(aData, f);
-    *f << "\n";
-  }
-
-  delete f;
-}
-
-static void UpdateEventFile(const Json::Value& aExtraData, const string& aHash,
-                            const string& aPingUuid) {
-  if (gEventsPath.empty()) {
-    // If there is no path for finding the crash event, skip this step.
-    return;
-  }
-
-  string localId = CrashReporter::GetDumpLocalID();
-  string path = gEventsPath + UI_DIR_SEPARATOR + localId;
-  string eventVersion;
-  string crashTime;
-  string crashUuid;
-  Json::Value eventData;
-
-  if (!ReadEventFile(path, eventVersion, crashTime, crashUuid, eventData)) {
-    return;
-  }
-
-  if (!aHash.empty()) {
-    eventData["MinidumpSha256Hash"] = aHash;
-  }
-
-  if (!aPingUuid.empty()) {
-    eventData["CrashPingUUID"] = aPingUuid;
-  }
-
-  if (aExtraData.isMember("StackTraces")) {
-    eventData["StackTraces"] = aExtraData["StackTraces"];
-  }
-
-  OverwriteEventFile(path, eventVersion, crashTime, crashUuid, eventData);
-}
-
-static void WriteSubmissionEvent(SubmissionResult result,
-                                 const string& remoteId) {
-  if (gEventsPath.empty()) {
-    // If there is no path for writing the submission event, skip it.
-    return;
-  }
-
-  string localId = CrashReporter::GetDumpLocalID();
-  string fpath = gEventsPath + UI_DIR_SEPARATOR + localId + "-submission";
-  ofstream* f = UIOpenWrite(fpath, ios::binary);
-  time_t tm;
-  time(&tm);
-
-  if (f->is_open()) {
-    *f << "crash.submission.1\n";
-    *f << tm << "\n";
-    *f << localId << "\n";
-    *f << (result == Succeeded ? "true" : "false") << "\n";
-    *f << remoteId;
-
-    f->close();
-  }
-
-  delete f;
-}
-
-void LogMessage(const std::string& message) {
-  if (gLogStream.get()) {
-    char date[64];
-    time_t tm;
-    time(&tm);
-    if (strftime(date, sizeof(date) - 1, "%c", localtime(&tm)) == 0)
-      date[0] = '\0';
-    (*gLogStream) << "[" << date << "] " << message << '\n';
-  }
-}
-
-static void OpenLogFile() {
-  string logPath = gSettingsPath + UI_DIR_SEPARATOR + "submit.log";
-  gLogStream.reset(UIOpenWrite(logPath, ios::app));
-}
-
-static bool ReadConfig() {
-  string iniPath;
-  if (!UIGetIniPath(iniPath)) {
-    return false;
-  }
-
-  if (!ReadStringsFromFile(iniPath, gStrings, true)) return false;
-
-  // See if we have a string override file, if so process it
-  char* overrideEnv = getenv("MOZ_CRASHREPORTER_STRINGS_OVERRIDE");
-  if (overrideEnv && *overrideEnv && UIFileExists(overrideEnv))
-    ReadStringsFromFile(overrideEnv, gStrings, true);
-
-  return true;
-}
-
-static string GetAdditionalFilename(const string& dumpfile,
-                                    const char* extension) {
-  string filename(dumpfile);
-  int dot = filename.rfind('.');
-  if (dot < 0) return "";
-
-  filename.replace(dot, filename.length() - dot, extension);
-  return filename;
-}
-
-static bool MoveCrashData(const string& toDir, string& dumpfile,
-                          string& extrafile, string& memoryfile) {
-  if (!UIEnsurePathExists(toDir)) {
-    UIError(gStrings[ST_ERROR_CREATEDUMPDIR]);
-    return false;
-  }
-
-  string newDump = toDir + UI_DIR_SEPARATOR + Basename(dumpfile);
-  string newExtra = toDir + UI_DIR_SEPARATOR + Basename(extrafile);
-  string newMemory = toDir + UI_DIR_SEPARATOR + Basename(memoryfile);
-
-  if (!UIMoveFile(dumpfile, newDump)) {
-    UIError(gStrings[ST_ERROR_DUMPFILEMOVE]);
-    return false;
-  }
-
-  if (!UIMoveFile(extrafile, newExtra)) {
-    UIError(gStrings[ST_ERROR_EXTRAFILEMOVE]);
-    return false;
-  }
-
-  if (!memoryfile.empty()) {
-    // Ignore errors from moving the memory file
-    if (!UIMoveFile(memoryfile, newMemory)) {
-      UIDeleteFile(memoryfile);
-      newMemory.erase();
-    }
-    memoryfile = newMemory;
-  }
-
-  dumpfile = newDump;
-  extrafile = newExtra;
-
-  return true;
-}
-
-static bool AddSubmittedReport(const string& serverResponse) {
-  StringTable responseItems;
-  istringstream in(serverResponse);
-  ReadStrings(in, responseItems, false);
-
-  if (responseItems.find("StopSendingReportsFor") != responseItems.end()) {
-    // server wants to tell us to stop sending reports for a certain version
-    string reportPath = gSettingsPath + UI_DIR_SEPARATOR + "EndOfLife" +
-                        responseItems["StopSendingReportsFor"];
-
-    ofstream* reportFile = UIOpenWrite(reportPath, ios::trunc);
-    if (reportFile->is_open()) {
-      // don't really care about the contents
-      *reportFile << 1 << "\n";
-      reportFile->close();
-    }
-    delete reportFile;
-  }
-
-  if (responseItems.find("Discarded") != responseItems.end()) {
-    // server discarded this report... save it so the user can resubmit it
-    // manually
-    return false;
-  }
-
-  if (responseItems.find("CrashID") == responseItems.end()) return false;
-
-  string submittedDir = gSettingsPath + UI_DIR_SEPARATOR + "submitted";
-  if (!UIEnsurePathExists(submittedDir)) {
-    return false;
-  }
-
-  string path =
-      submittedDir + UI_DIR_SEPARATOR + responseItems["CrashID"] + ".txt";
-
-  ofstream* file = UIOpenWrite(path, ios::trunc);
-  if (!file->is_open()) {
-    delete file;
-    return false;
-  }
-
-  char buf[1024];
-  snprintf(buf, 1024, gStrings["CrashID"].c_str(),
-           responseItems["CrashID"].c_str());
-  *file << buf << "\n";
-
-  if (responseItems.find("ViewURL") != responseItems.end()) {
-    snprintf(buf, 1024, gStrings["CrashDetailsURL"].c_str(),
-             responseItems["ViewURL"].c_str());
-    *file << buf << "\n";
-  }
-
-  file->close();
-  delete file;
-
-  WriteSubmissionEvent(Succeeded, responseItems["CrashID"]);
-  return true;
-}
-
-void DeleteDump() {
-  const char* noDelete = getenv("MOZ_CRASHREPORTER_NO_DELETE_DUMP");
-  if (!noDelete || *noDelete == '\0') {
-    if (!gReporterDumpFile.empty()) UIDeleteFile(gReporterDumpFile);
-    if (!gExtraFile.empty()) UIDeleteFile(gExtraFile);
-    if (!gMemoryFile.empty()) UIDeleteFile(gMemoryFile);
-  }
-}
-
-void SendCompleted(bool success, const string& serverResponse) {
-  if (success) {
-    if (AddSubmittedReport(serverResponse)) {
-      DeleteDump();
-    } else {
-      string directory = gReporterDumpFile;
-      int slashpos = directory.find_last_of("/\\");
-      if (slashpos < 2) return;
-      directory.resize(slashpos);
-      UIPruneSavedDumps(directory);
-      WriteSubmissionEvent(Failed, "");
-    }
-  } else {
-    WriteSubmissionEvent(Failed, "");
-  }
-}
-
-static string ComputeDumpHash() {
-#ifdef XP_LINUX
-  // On Linux we rely on the system-provided libcurl which uses nss so we have
-  // to also use the system-provided nss instead of the ones we have bundled.
-  const char* libnssNames[] = {
-      "libnss3.so",
-#  ifndef HAVE_64BIT_BUILD
-      // 32-bit versions on 64-bit hosts
-      "/usr/lib32/libnss3.so",
-#  endif
-  };
-  void* lib = nullptr;
-
-  for (const char* libname : libnssNames) {
-    lib = dlopen(libname, RTLD_NOW);
-
-    if (lib) {
-      break;
-    }
-  }
-
-  if (!lib) {
-    return "";
-  }
-
-  SECStatus (*NSS_Initialize)(const char*, const char*, const char*,
-                              const char*, PRUint32);
-  HASHContext* (*HASH_Create)(HASH_HashType);
-  void (*HASH_Destroy)(HASHContext*);
-  void (*HASH_Begin)(HASHContext*);
-  void (*HASH_Update)(HASHContext*, const unsigned char*, unsigned int);
-  void (*HASH_End)(HASHContext*, unsigned char*, unsigned int*, unsigned int);
-
-  *(void**)(&NSS_Initialize) = dlsym(lib, "NSS_Initialize");
-  *(void**)(&HASH_Create) = dlsym(lib, "HASH_Create");
-  *(void**)(&HASH_Destroy) = dlsym(lib, "HASH_Destroy");
-  *(void**)(&HASH_Begin) = dlsym(lib, "HASH_Begin");
-  *(void**)(&HASH_Update) = dlsym(lib, "HASH_Update");
-  *(void**)(&HASH_End) = dlsym(lib, "HASH_End");
-
-  if (!HASH_Create || !HASH_Destroy || !HASH_Begin || !HASH_Update ||
-      !HASH_End) {
-    return "";
-  }
-#endif
-  // Minimal NSS initialization so we can use the hash functions
-  const PRUint32 kNssFlags = NSS_INIT_READONLY | NSS_INIT_NOROOTINIT |
-                             NSS_INIT_NOMODDB | NSS_INIT_NOCERTDB;
-  if (NSS_Initialize(nullptr, "", "", "", kNssFlags) != SECSuccess) {
-    return "";
-  }
-
-  HASHContext* hashContext = HASH_Create(HASH_AlgSHA256);
-
-  if (!hashContext) {
-    return "";
-  }
-
-  HASH_Begin(hashContext);
-
-  ifstream* f = UIOpenRead(gReporterDumpFile, ios::binary);
-  bool error = false;
-
-  // Read the minidump contents
-  if (f->is_open()) {
-    uint8_t buff[4096];
-
-    do {
-      f->read((char*)buff, sizeof(buff));
-
-      if (f->bad()) {
-        error = true;
-        break;
-      }
-
-      HASH_Update(hashContext, buff, f->gcount());
-    } while (!f->eof());
-
-    f->close();
-  } else {
-    error = true;
-  }
-
-  delete f;
-
-  // Finalize the hash computation
-  uint8_t result[SHA256_LENGTH];
-  uint32_t resultLen = 0;
-
-  HASH_End(hashContext, result, &resultLen, SHA256_LENGTH);
-
-  if (resultLen != SHA256_LENGTH) {
-    error = true;
-  }
-
-  HASH_Destroy(hashContext);
-
-  if (!error) {
-    ostringstream hash;
-
-    for (size_t i = 0; i < SHA256_LENGTH; i++) {
-      hash << std::setw(2) << std::setfill('0') << std::hex
-           << static_cast<unsigned int>(result[i]);
-    }
-
-    return hash.str();
-  }
-  return "";  // If we encountered an error, return an empty hash
-}
-
-string GetDumpLocalID() {
-  string localId = Basename(gReporterDumpFile);
-  string::size_type dot = localId.rfind('.');
-
-  if (dot == string::npos) return "";
-
-  return localId.substr(0, dot);
-}
-
-string GetProgramPath(const string& exename) {
-  string path = gArgv[0];
-  size_t pos = path.rfind(UI_CRASH_REPORTER_FILENAME BIN_SUFFIX);
-  path.erase(pos);
-#ifdef XP_MACOSX
-  // On macOS the crash reporter client is shipped as an application bundle
-  // contained within Firefox' main application bundle. So when it's invoked
-  // its current working directory looks like:
-  // Firefox.app/Contents/MacOS/crashreporter.app/Contents/MacOS/
-  // The other applications we ship with Firefox are stored in the main bundle
-  // (Firefox.app/Contents/MacOS/) so we we need to go back three directories
-  // to reach them.
-  path.erase(pos - 1);
-  for (size_t i = 0; i < 3; i++) {
-    pos = path.rfind(UI_DIR_SEPARATOR, pos - 1);
-  }
-
-  path.erase(pos + 1);
-#endif  // XP_MACOSX
-  path.append(exename + BIN_SUFFIX);
-
-  return path;
-}
-
-}  // namespace CrashReporter
-
-using namespace CrashReporter;
-
-Json::Value kEmptyJsonString("");
-
-void RewriteStrings(Json::Value& aExtraData) {
-  // rewrite some UI strings with the values from the query parameters
-  string product = aExtraData.get("ProductName", kEmptyJsonString).asString();
-  Json::Value mozilla("Mozilla");
-  string vendor = aExtraData.get("Vendor", mozilla).asString();
-
-  char buf[4096];
-  snprintf(buf, sizeof(buf), gStrings[ST_CRASHREPORTERVENDORTITLE].c_str(),
-           vendor.c_str());
-  gStrings[ST_CRASHREPORTERTITLE] = buf;
-
-  string str = gStrings[ST_CRASHREPORTERPRODUCTERROR];
-  // Only do the replacement here if the string has two
-  // format specifiers to start.  Otherwise
-  // we assume it has the product name hardcoded.
-  string::size_type pos = str.find("%s");
-  if (pos != string::npos) pos = str.find("%s", pos + 2);
-  if (pos != string::npos) {
-    // Leave a format specifier for UIError to fill in
-    snprintf(buf, sizeof(buf), gStrings[ST_CRASHREPORTERPRODUCTERROR].c_str(),
-             product.c_str(), "%s");
-    gStrings[ST_CRASHREPORTERERROR] = buf;
-  } else {
-    // product name is hardcoded
-    gStrings[ST_CRASHREPORTERERROR] = str;
-  }
-
-  snprintf(buf, sizeof(buf), gStrings[ST_CRASHREPORTERDESCRIPTION].c_str(),
-           product.c_str());
-  gStrings[ST_CRASHREPORTERDESCRIPTION] = buf;
-
-  snprintf(buf, sizeof(buf), gStrings[ST_CHECKSUBMIT].c_str(), vendor.c_str());
-  gStrings[ST_CHECKSUBMIT] = buf;
-
-  snprintf(buf, sizeof(buf), gStrings[ST_RESTART].c_str(), product.c_str());
-  gStrings[ST_RESTART] = buf;
-
-  snprintf(buf, sizeof(buf), gStrings[ST_QUIT].c_str(), product.c_str());
-  gStrings[ST_QUIT] = buf;
-
-  snprintf(buf, sizeof(buf), gStrings[ST_ERROR_ENDOFLIFE].c_str(),
-           product.c_str());
-  gStrings[ST_ERROR_ENDOFLIFE] = buf;
-}
-
-bool CheckEndOfLifed(const Json::Value& aVersion) {
-  if (!aVersion.isString()) {
-    return false;
-  }
-
-  string reportPath =
-      gSettingsPath + UI_DIR_SEPARATOR + "EndOfLife" + aVersion.asString();
-  return UIFileExists(reportPath);
-}
-
-int main(int argc, char** argv) {
-  gArgc = argc;
-  gArgv = argv;
-
-  string autoSubmitEnv = UIGetEnv("MOZ_CRASHREPORTER_AUTO_SUBMIT");
-  gAutoSubmit = !autoSubmitEnv.empty();
-
-  if (!ReadConfig()) {
-    UIError("Couldn't read configuration.");
-    return 0;
-  }
-
-  if (!UIInit()) {
-    return 0;
-  }
-
-  if (argc > 1) {
-    gReporterDumpFile = argv[1];
-  }
-
-  if (gReporterDumpFile.empty()) {
-    // no dump file specified, run the default UI
-    if (!gAutoSubmit) {
-      UIShowDefaultUI();
-    }
-  } else {
-    // Start by running minidump analyzer to gather stack traces.
-    string reporterDumpFile = gReporterDumpFile;
-    vector<string> args = {reporterDumpFile};
-    string dumpAllThreadsEnv = UIGetEnv("MOZ_CRASHREPORTER_DUMP_ALL_THREADS");
-    if (!dumpAllThreadsEnv.empty()) {
-      args.insert(args.begin(), "--full");
-    }
-    UIRunProgram(CrashReporter::GetProgramPath(UI_MINIDUMP_ANALYZER_FILENAME),
-                 args,
-                 /* wait */ true);
-
-    // go ahead with the crash reporter
-    gExtraFile = GetAdditionalFilename(gReporterDumpFile, kExtraDataExtension);
-    if (gExtraFile.empty()) {
-      UIError(gStrings[ST_ERROR_BADARGUMENTS]);
-      return 0;
-    }
-
-    if (!UIFileExists(gExtraFile)) {
-      UIError(gStrings[ST_ERROR_EXTRAFILEEXISTS]);
-      return 0;
-    }
-
-    gMemoryFile =
-        GetAdditionalFilename(gReporterDumpFile, kMemoryReportExtension);
-    if (!UIFileExists(gMemoryFile)) {
-      gMemoryFile.erase();
-    }
-
-    Json::Value extraData;
-    if (!ReadExtraFile(gExtraFile, extraData)) {
-      UIError(gStrings[ST_ERROR_EXTRAFILEREAD]);
-      return 0;
-    }
-
-    if (!extraData.isMember("ProductName")) {
-      UIError(gStrings[ST_ERROR_NOPRODUCTNAME]);
-      return 0;
-    }
-
-    // There is enough information in the extra file to rewrite strings
-    // to be product specific
-    RewriteStrings(extraData);
-
-    if (!extraData.isMember("ServerURL")) {
-      UIError(gStrings[ST_ERROR_NOSERVERURL]);
-      return 0;
-    }
-
-    // Hopefully the settings path exists in the environment. Try that before
-    // asking the platform-specific code to guess.
-    gSettingsPath = UIGetEnv("MOZ_CRASHREPORTER_DATA_DIRECTORY");
-    if (gSettingsPath.empty()) {
-      string product =
-          extraData.get("ProductName", kEmptyJsonString).asString();
-      string vendor = extraData.get("Vendor", kEmptyJsonString).asString();
-
-      if (!UIGetSettingsPath(vendor, product, gSettingsPath)) {
-        gSettingsPath.clear();
-      }
-    }
-
-    if (gSettingsPath.empty() || !UIEnsurePathExists(gSettingsPath)) {
-      UIError(gStrings[ST_ERROR_NOSETTINGSPATH]);
-      return 0;
-    }
-
-    OpenLogFile();
-
-    gEventsPath = UIGetEnv("MOZ_CRASHREPORTER_EVENTS_DIRECTORY");
-    gPingPath = UIGetEnv("MOZ_CRASHREPORTER_PING_DIRECTORY");
-
-    // Assemble and send the crash ping
-    string hash = ComputeDumpHash();
-
-    string pingUuid;
-    SendCrashPing(extraData, hash, pingUuid, gPingPath);
-    UpdateEventFile(extraData, hash, pingUuid);
-
-    if (!UIFileExists(gReporterDumpFile)) {
-      UIError(gStrings[ST_ERROR_DUMPFILEEXISTS]);
-      return 0;
-    }
-
-    string pendingDir = gSettingsPath + UI_DIR_SEPARATOR + "pending";
-    if (!MoveCrashData(pendingDir, gReporterDumpFile, gExtraFile,
-                       gMemoryFile)) {
-      return 0;
-    }
-
-    string sendURL = extraData.get("ServerURL", kEmptyJsonString).asString();
-    // we don't need to actually send these
-    extraData.removeMember("ServerURL");
-    extraData.removeMember("StackTraces");
-
-    extraData["SubmittedFrom"] = "Client";
-    extraData["Throttleable"] = "1";
-
-    // re-set XUL_APP_FILE for xulrunner wrapped apps
-    const char* appfile = getenv("MOZ_CRASHREPORTER_RESTART_XUL_APP_FILE");
-    if (appfile && *appfile) {
-      const char prefix[] = "XUL_APP_FILE=";
-      char* env = (char*)malloc(strlen(appfile) + strlen(prefix) + 1);
-      if (!env) {
-        UIError("Out of memory");
-        return 0;
-      }
-      strcpy(env, prefix);
-      strcat(env, appfile);
-      putenv(env);
-      free(env);
-    }
-
-    vector<string> restartArgs;
-
-    if (!extraData.isMember("WindowsErrorReporting")) {
-      // We relaunch the application associated with the client, but only when
-      // we encountered a crash caught by the exception handler. Crashes handled
-      // by WER are prevented from directly restarting the application.
-      string programPath = GetProgramPath(MOZ_APP_NAME);
-#ifndef XP_WIN
-      const char* moz_app_launcher = getenv("MOZ_APP_LAUNCHER");
-      if (moz_app_launcher) {
-        programPath = moz_app_launcher;
-      }
-#endif  // XP_WIN
-
-      restartArgs.push_back(programPath);
-
-      ostringstream paramName;
-      int i = 1;
-      paramName << "MOZ_CRASHREPORTER_RESTART_ARG_" << i++;
-      const char* param = getenv(paramName.str().c_str());
-      while (param && *param) {
-        restartArgs.push_back(param);
-
-        paramName.str("");
-        paramName << "MOZ_CRASHREPORTER_RESTART_ARG_" << i++;
-        param = getenv(paramName.str().c_str());
-      }
-    }
-
-    // allow override of the server url via environment variable
-    // XXX: remove this in the far future when our robot
-    // masters force everyone to use XULRunner
-    char* urlEnv = getenv("MOZ_CRASHREPORTER_URL");
-    if (urlEnv && *urlEnv) {
-      sendURL = urlEnv;
-    }
-
-    // see if this version has been end-of-lifed
-
-    if (extraData.isMember("Version") &&
-        CheckEndOfLifed(extraData["Version"])) {
-      UIError(gStrings[ST_ERROR_ENDOFLIFE]);
-      DeleteDump();
-      return 0;
-    }
-
-    StringTable files;
-    files["upload_file_minidump"] = gReporterDumpFile;
-    if (!gMemoryFile.empty()) {
-      files["memory_report"] = gMemoryFile;
-    }
-
-    if (!UIShowCrashUI(files, extraData, sendURL, restartArgs)) {
-      DeleteDump();
-    }
-  }
-
-  UIShutdown();
-
-  return 0;
-}
-
-#if defined(XP_WIN) && !defined(__GNUC__)
-#  include <windows.h>
-
-// We need WinMain in order to not be a console app.  This function is unused
-// if we are a console application.
-int WINAPI wWinMain(HINSTANCE, HINSTANCE, LPWSTR args, int) {
-  // Remove everything except close window from the context menu
-  {
-    HKEY hkApp;
-    RegCreateKeyExW(HKEY_CURRENT_USER, L"Software\\Classes\\Applications", 0,
-                    nullptr, REG_OPTION_NON_VOLATILE, KEY_SET_VALUE, nullptr,
-                    &hkApp, nullptr);
-    RegCloseKey(hkApp);
-    if (RegCreateKeyExW(HKEY_CURRENT_USER,
-                        L"Software\\Classes\\Applications\\crashreporter.exe",
-                        0, nullptr, REG_OPTION_VOLATILE, KEY_SET_VALUE, nullptr,
-                        &hkApp, nullptr) == ERROR_SUCCESS) {
-      RegSetValueExW(hkApp, L"IsHostApp", 0, REG_NONE, 0, 0);
-      RegSetValueExW(hkApp, L"NoOpenWith", 0, REG_NONE, 0, 0);
-      RegSetValueExW(hkApp, L"NoStartPage", 0, REG_NONE, 0, 0);
-      RegCloseKey(hkApp);
-    }
-  }
-
-  char** argv = static_cast<char**>(malloc(__argc * sizeof(char*)));
-  for (int i = 0; i < __argc; i++) {
-    argv[i] = strdup(WideToUTF8(__wargv[i]).c_str());
-  }
-
-  // Do the real work.
-  return main(__argc, argv);
-}
-#endif
diff --git a/toolkit/crashreporter/client/crashreporter.exe.manifest b/toolkit/crashreporter/client/crashreporter.exe.manifest
deleted file mode 100644
index 81aa1465c6..0000000000
--- a/toolkit/crashreporter/client/crashreporter.exe.manifest
+++ /dev/null
@@ -1,42 +0,0 @@
-<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
-<assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0">
-<assemblyIdentity
-        version="1.0.0.0"
-        processorArchitecture="*"
-        name="CrashReporter"
-        type="win32"
-/>
-<description>Crash Reporter</description>
-<dependency>
-        <dependentAssembly>
-                <assemblyIdentity
-                        type="win32"
-                        name="Microsoft.Windows.Common-Controls"
-                        version="6.0.0.0"
-                        processorArchitecture="*"
-                        publicKeyToken="6595b64144ccf1df"
-                        language="*"
-                />
-        </dependentAssembly>
-</dependency>
-<ms_asmv3:trustInfo xmlns:ms_asmv3="urn:schemas-microsoft-com:asm.v3">
-  <ms_asmv3:security>
-    <ms_asmv3:requestedPrivileges>
-      <ms_asmv3:requestedExecutionLevel level="asInvoker" uiAccess="false" />
-    </ms_asmv3:requestedPrivileges>
-  </ms_asmv3:security>
-</ms_asmv3:trustInfo>
-  <ms_asmv3:application xmlns:ms_asmv3="urn:schemas-microsoft-com:asm.v3">
-    <ms_asmv3:windowsSettings xmlns="http://schemas.microsoft.com/SMI/2005/WindowsSettings">
-      <gdiScaling xmlns="http://schemas.microsoft.com/SMI/2017/WindowsSettings">true</gdiScaling>
-    </ms_asmv3:windowsSettings>
-  </ms_asmv3:application>
-  <compatibility xmlns="urn:schemas-microsoft-com:compatibility.v1">
-    <application>
-      <supportedOS Id="{8e0f7a12-bfb3-4fe8-b9a5-48fd50a15a9a}"/>
-      <supportedOS Id="{1f676c76-80e1-4239-95bb-83d0f6d0da78}"/>
-      <supportedOS Id="{4a2f28e3-53b9-4441-ba9c-d69d4a4a6e38}"/>
-      <supportedOS Id="{35138b9a-5d96-4fbd-8e2d-a2440225f93a}"/>
-    </application>
-  </compatibility>
-</assembly>
diff --git a/toolkit/crashreporter/client/crashreporter.h b/toolkit/crashreporter/client/crashreporter.h
deleted file mode 100644
index fa7085da18..0000000000
--- a/toolkit/crashreporter/client/crashreporter.h
+++ /dev/null
@@ -1,158 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-#ifndef CRASHREPORTER_H__
-#define CRASHREPORTER_H__
-
-#ifdef _MSC_VER
-#  pragma warning(push)
-// Disable exception handler warnings.
-#  pragma warning(disable : 4530)
-#endif
-
-#include <string>
-#include <map>
-#include <vector>
-#include <stdlib.h>
-#include <stdio.h>
-#include <fstream>
-
-#define MAX_COMMENT_LENGTH 10000
-
-#if defined(XP_WIN)
-
-#  include <windows.h>
-
-#  define UI_DIR_SEPARATOR "\\"
-
-std::string WideToUTF8(const std::wstring& wide, bool* success = 0);
-
-#else
-
-#  define UI_DIR_SEPARATOR "/"
-
-#endif
-
-#include "json/json.h"
-
-#define UI_CRASH_REPORTER_FILENAME "crashreporter"
-#define UI_MINIDUMP_ANALYZER_FILENAME "minidump-analyzer"
-#define UI_PING_SENDER_FILENAME "pingsender"
-
-typedef std::map<std::string, std::string> StringTable;
-
-#define ST_CRASHREPORTERTITLE "CrashReporterTitle"
-#define ST_CRASHREPORTERVENDORTITLE "CrashReporterVendorTitle"
-#define ST_CRASHREPORTERERROR "CrashReporterErrorText"
-#define ST_CRASHREPORTERPRODUCTERROR "CrashReporterProductErrorText2"
-#define ST_CRASHREPORTERHEADER "CrashReporterSorry"
-#define ST_CRASHREPORTERDESCRIPTION "CrashReporterDescriptionText2"
-#define ST_CRASHREPORTERDEFAULT "CrashReporterDefault"
-#define ST_VIEWREPORT "Details"
-#define ST_VIEWREPORTTITLE "ViewReportTitle"
-#define ST_COMMENTGRAYTEXT "CommentGrayText"
-#define ST_EXTRAREPORTINFO "ExtraReportInfo"
-#define ST_CHECKSUBMIT "CheckSendReport"
-#define ST_CHECKURL "CheckIncludeURL"
-#define ST_REPORTPRESUBMIT "ReportPreSubmit2"
-#define ST_REPORTDURINGSUBMIT "ReportDuringSubmit2"
-#define ST_REPORTSUBMITSUCCESS "ReportSubmitSuccess"
-#define ST_SUBMITFAILED "ReportSubmitFailed"
-#define ST_QUIT "Quit2"
-#define ST_RESTART "Restart"
-#define ST_OK "Ok"
-#define ST_CLOSE "Close"
-
-#define ST_ERROR_BADARGUMENTS "ErrorBadArguments"
-#define ST_ERROR_EXTRAFILEEXISTS "ErrorExtraFileExists"
-#define ST_ERROR_EXTRAFILEREAD "ErrorExtraFileRead"
-#define ST_ERROR_EXTRAFILEMOVE "ErrorExtraFileMove"
-#define ST_ERROR_DUMPFILEEXISTS "ErrorDumpFileExists"
-#define ST_ERROR_DUMPFILEMOVE "ErrorDumpFileMove"
-#define ST_ERROR_NOPRODUCTNAME "ErrorNoProductName"
-#define ST_ERROR_NOSERVERURL "ErrorNoServerURL"
-#define ST_ERROR_NOSETTINGSPATH "ErrorNoSettingsPath"
-#define ST_ERROR_CREATEDUMPDIR "ErrorCreateDumpDir"
-#define ST_ERROR_ENDOFLIFE "ErrorEndOfLife"
-
-//=============================================================================
-// implemented in crashreporter.cpp and ping.cpp
-//=============================================================================
-
-namespace CrashReporter {
-extern StringTable gStrings;
-extern std::string gSettingsPath;
-extern std::string gEventsPath;
-extern int gArgc;
-extern char** gArgv;
-extern bool gAutoSubmit;
-
-void UIError(const std::string& message);
-
-// The UI finished sending the report
-void SendCompleted(bool success, const std::string& serverResponse);
-
-bool ReadStrings(std::istream& in, StringTable& strings, bool unescape);
-bool ReadStringsFromFile(const std::string& path, StringTable& strings,
-                         bool unescape);
-void LogMessage(const std::string& message);
-void DeleteDump();
-
-std::string GetDumpLocalID();
-std::string GetProgramPath(const std::string& exename);
-
-// Telemetry ping
-bool SendCrashPing(Json::Value& extra, const std::string& hash,
-                   std::string& pingUuid, const std::string& pingDir);
-
-static const unsigned int kSaveCount = 10;
-}  // namespace CrashReporter
-
-//=============================================================================
-// implemented in the platform-specific files
-//=============================================================================
-
-bool UIInit();
-void UIShutdown();
-
-// Run the UI for when the app was launched without a dump file
-void UIShowDefaultUI();
-
-// Run the UI for when the app was launched with a dump file
-// Return true if the user sent (or tried to send) the crash report,
-// false if they chose not to, and it should be deleted.
-bool UIShowCrashUI(const StringTable& files, const Json::Value& queryParameters,
-                   const std::string& sendURL,
-                   const std::vector<std::string>& restartArgs);
-
-void UIError_impl(const std::string& message);
-
-bool UIGetIniPath(std::string& path);
-bool UIGetSettingsPath(const std::string& vendor, const std::string& product,
-                       std::string& settingsPath);
-bool UIEnsurePathExists(const std::string& path);
-bool UIFileExists(const std::string& path);
-bool UIMoveFile(const std::string& oldfile, const std::string& newfile);
-bool UIDeleteFile(const std::string& oldfile);
-std::ifstream* UIOpenRead(const std::string& filename,
-                          std::ios_base::openmode mode);
-std::ofstream* UIOpenWrite(const std::string& filename,
-                           std::ios_base::openmode mode);
-void UIPruneSavedDumps(const std::string& directory);
-
-// Run the program specified by exename, passing it the parameters in arg.
-// If wait is true, wait for the program to terminate execution before
-// returning. Returns true if the program was launched correctly, false
-// otherwise.
-bool UIRunProgram(const std::string& exename,
-                  const std::vector<std::string>& args, bool wait = false);
-
-// Read the environment variable specified by name
-std::string UIGetEnv(const std::string& name);
-
-#ifdef _MSC_VER
-#  pragma warning(pop)
-#endif
-
-#endif
diff --git a/toolkit/crashreporter/client/crashreporter.ico b/toolkit/crashreporter/client/crashreporter.ico
deleted file mode 100644
index 29ac3c6189..0000000000
--- a/toolkit/crashreporter/client/crashreporter.ico
+++ /dev/null
diff --git a/toolkit/crashreporter/client/crashreporter.rc b/toolkit/crashreporter/client/crashreporter.rc
deleted file mode 100755
index f6042bf2e5..0000000000
--- a/toolkit/crashreporter/client/crashreporter.rc
+++ /dev/null
@@ -1,143 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-// Microsoft Visual C++ generated resource script.
-//
-#include "resource.h"
-
-#define APSTUDIO_READONLY_SYMBOLS
-/////////////////////////////////////////////////////////////////////////////
-//
-// Generated from the TEXTINCLUDE 2 resource.
-//
-#include "winresrc.h"
-
-/////////////////////////////////////////////////////////////////////////////
-#undef APSTUDIO_READONLY_SYMBOLS
-
-/////////////////////////////////////////////////////////////////////////////
-// English (U.S.) resources
-
-#if !defined(AFX_RESOURCE_DLL) || defined(AFX_TARG_ENU)
-#ifdef _WIN32
-LANGUAGE LANG_ENGLISH, SUBLANG_ENGLISH_US
-#pragma code_page(1252)
-#endif //_WIN32
-
-#ifdef APSTUDIO_INVOKED
-/////////////////////////////////////////////////////////////////////////////
-//
-// TEXTINCLUDE
-//
-
-1 TEXTINCLUDE 
-BEGIN
-    "resource.h\0"
-END
-
-2 TEXTINCLUDE 
-BEGIN
-    "#include ""winresrc.h""\r\n"
-    "\0"
-END
-
-3 TEXTINCLUDE 
-BEGIN
-    "\r\n"
-    "\0"
-END
-
-#endif    // APSTUDIO_INVOKED
-
-/////////////////////////////////////////////////////////////////////////////
-//
-// Icon
-//
-
-// Icon with lowest ID value placed first to ensure application icon
-// remains consistent on all systems.
-IDI_MAINICON            ICON                    "crashreporter.ico"
-
-/////////////////////////////////////////////////////////////////////////////
-//
-// AVI
-//
-
-IDR_THROBBER            AVI                     "Throbber-small.avi"
-
-/////////////////////////////////////////////////////////////////////////////
-//
-// Dialog
-//
-
-IDD_SENDDIALOG DIALOGEX 0, 0, 241, 187
-STYLE DS_SETFONT | DS_MODALFRAME | DS_FIXEDSYS | DS_CENTER | WS_POPUP | WS_VISIBLE | WS_CAPTION | WS_SYSMENU
-EXSTYLE WS_EX_APPWINDOW
-CAPTION "Sending Crash Report..."
-FONT 8, "MS Shell Dlg", 400, 0, 0x1
-BEGIN
-    CONTROL         "",IDC_DESCRIPTIONTEXT,"RICHEDIT50W",ES_MULTILINE | ES_READONLY,8,7,226,12,WS_EX_TRANSPARENT
-    CONTROL         "tell mozilla about this crash so they can fix it",IDC_SUBMITREPORTCHECK,
-                    "Button",BS_AUTOCHECKBOX | WS_TABSTOP,12,25,222,10
-    CHECKBOX        "details...",IDC_VIEWREPORTBUTTON,24,40,54,14,BS_PUSHLIKE
-    EDITTEXT        IDC_COMMENTTEXT,24,59,210,43,ES_MULTILINE | ES_WANTRETURN | WS_VSCROLL
-    CONTROL         "include the address of the page i was on",IDC_INCLUDEURLCHECK,
-                    "Button",BS_AUTOCHECKBOX | WS_TABSTOP,24,107,210,10
-    CONTROL         "",IDC_THROBBER,"SysAnimate32",ACS_TRANSPARENT | NOT WS_VISIBLE | WS_TABSTOP,4,152,16,16
-    LTEXT           "your crash report will be submitted when you restart",IDC_PROGRESSTEXT,24,152,210,10,SS_NOPREFIX
-    DEFPUSHBUTTON   "restart firefox",IDC_RESTARTBUTTON,84,166,68,14
-    PUSHBUTTON      "quit without sending",IDC_CLOSEBUTTON,157,166,77,14
-END
-
-IDD_VIEWREPORTDIALOG DIALOGEX 0, 0, 208, 126
-STYLE DS_SETFONT | DS_MODALFRAME | DS_FIXEDSYS | DS_CENTER | WS_POPUP | WS_CAPTION
-CAPTION "view report"
-FONT 8, "MS Shell Dlg", 400, 0, 0x1
-BEGIN
-    CONTROL         "",IDC_VIEWREPORTTEXT,"RICHEDIT50W",ES_MULTILINE | ES_READONLY | WS_BORDER | WS_VSCROLL | WS_TABSTOP,7,7,194,92
-    DEFPUSHBUTTON   "OK",IDOK,151,105,50,14
-END
-
-
-/////////////////////////////////////////////////////////////////////////////
-//
-// DESIGNINFO
-//
-
-#ifdef APSTUDIO_INVOKED
-GUIDELINES DESIGNINFO 
-BEGIN
-    IDD_SENDDIALOG, DIALOG
-    BEGIN
-        LEFTMARGIN, 8
-        RIGHTMARGIN, 234
-        TOPMARGIN, 7
-        BOTTOMMARGIN, 180
-    END
-
-    IDD_VIEWREPORTDIALOG, DIALOG
-    BEGIN
-        LEFTMARGIN, 7
-        RIGHTMARGIN, 201
-        TOPMARGIN, 7
-        BOTTOMMARGIN, 119
-    END
-END
-#endif    // APSTUDIO_INVOKED
-
-#endif    // English (U.S.) resources
-/////////////////////////////////////////////////////////////////////////////
-
-
-
-#ifndef APSTUDIO_INVOKED
-/////////////////////////////////////////////////////////////////////////////
-//
-// Generated from the TEXTINCLUDE 3 resource.
-//
-
-
-/////////////////////////////////////////////////////////////////////////////
-#endif    // not APSTUDIO_INVOKED
-
diff --git a/toolkit/crashreporter/client/crashreporter_gtk_common.cpp b/toolkit/crashreporter/client/crashreporter_gtk_common.cpp
deleted file mode 100644
index b9a957cfd9..0000000000
--- a/toolkit/crashreporter/client/crashreporter_gtk_common.cpp
+++ /dev/null
@@ -1,361 +0,0 @@
-/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-#include <unistd.h>
-#include <dlfcn.h>
-#include <errno.h>
-#include <glib.h>
-#include <gtk/gtk.h>
-#include <signal.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-#include <sys/stat.h>
-#include <sys/types.h>
-#include <sys/wait.h>
-#include <gdk/gdkkeysyms.h>
-
-#include <algorithm>
-#include <string>
-#include <vector>
-
-#include "common/linux/http_upload.h"
-#include "crashreporter.h"
-#include "crashreporter_gtk_common.h"
-
-#ifndef GDK_KEY_Escape
-#  define GDK_KEY_Escape GDK_Escape
-#endif
-
-using std::string;
-using std::vector;
-
-using namespace CrashReporter;
-
-GtkWidget* gWindow = 0;
-GtkWidget* gSubmitReportCheck = 0;
-GtkWidget* gIncludeURLCheck = 0;
-GtkWidget* gThrobber = 0;
-GtkWidget* gProgressLabel = 0;
-GtkWidget* gCloseButton = 0;
-GtkWidget* gRestartButton = 0;
-
-bool gInitialized = false;
-bool gDidTrySend = false;
-StringTable gFiles;
-Json::Value gQueryParameters;
-string gHttpProxy;
-string gAuth;
-string gCACertificateFile;
-string gSendURL;
-string gURLParameter;
-vector<string> gRestartArgs;
-GThread* gSendThreadID;
-
-// From crashreporter_linux.cpp
-void SendReport();
-void DisableGUIAndSendReport();
-void TryInitGnome();
-void UpdateSubmit();
-
-static bool RestartApplication() {
-  char** argv = reinterpret_cast<char**>(
-      malloc(sizeof(char*) * (gRestartArgs.size() + 1)));
-
-  if (!argv) return false;
-
-  unsigned int i;
-  for (i = 0; i < gRestartArgs.size(); i++) {
-    argv[i] = (char*)gRestartArgs[i].c_str();
-  }
-  argv[i] = 0;
-
-  pid_t pid = fork();
-  if (pid == -1) {
-    free(argv);
-    return false;
-  }
-
-  if (pid == 0) {
-    (void)execv(argv[0], argv);
-    _exit(1);
-  }
-
-  free(argv);
-
-  return true;
-}
-
-// Quit the app, used as a timeout callback
-gboolean CloseApp(gpointer data) {
-  if (!gAutoSubmit) {
-    gtk_main_quit();
-  }
-  g_thread_join(gSendThreadID);
-  return FALSE;
-}
-
-static gboolean ReportCompleted(gpointer success) {
-  gtk_widget_hide(gThrobber);
-  string str =
-      success ? gStrings[ST_REPORTSUBMITSUCCESS] : gStrings[ST_SUBMITFAILED];
-  gtk_label_set_text(GTK_LABEL(gProgressLabel), str.c_str());
-  g_timeout_add(5000, CloseApp, 0);
-  return FALSE;
-}
-
-#define HTTP_PROXY_DIR "/system/http_proxy"
-
-void LoadProxyinfo() {
-  class GConfClient;
-  typedef GConfClient* (*_gconf_default_fn)();
-  typedef gboolean (*_gconf_bool_fn)(GConfClient*, const gchar*, GError**);
-  typedef gint (*_gconf_int_fn)(GConfClient*, const gchar*, GError**);
-  typedef gchar* (*_gconf_string_fn)(GConfClient*, const gchar*, GError**);
-
-  if (getenv("http_proxy"))
-    return;  // libcurl can use the value from the environment
-
-  static void* gconfLib = dlopen("libgconf-2.so.4", RTLD_LAZY);
-  if (!gconfLib) return;
-
-  _gconf_default_fn gconf_client_get_default =
-      (_gconf_default_fn)dlsym(gconfLib, "gconf_client_get_default");
-  _gconf_bool_fn gconf_client_get_bool =
-      (_gconf_bool_fn)dlsym(gconfLib, "gconf_client_get_bool");
-  _gconf_int_fn gconf_client_get_int =
-      (_gconf_int_fn)dlsym(gconfLib, "gconf_client_get_int");
-  _gconf_string_fn gconf_client_get_string =
-      (_gconf_string_fn)dlsym(gconfLib, "gconf_client_get_string");
-
-  if (!(gconf_client_get_default && gconf_client_get_bool &&
-        gconf_client_get_int && gconf_client_get_string)) {
-    dlclose(gconfLib);
-    return;
-  }
-
-  GConfClient* conf = gconf_client_get_default();
-
-  if (gconf_client_get_bool(conf, HTTP_PROXY_DIR "/use_http_proxy", nullptr)) {
-    gint port;
-    gchar *host = nullptr, *httpproxy = nullptr;
-
-    host = gconf_client_get_string(conf, HTTP_PROXY_DIR "/host", nullptr);
-    port = gconf_client_get_int(conf, HTTP_PROXY_DIR "/port", nullptr);
-
-    if (port && host && *host != '\0') {
-      httpproxy = g_strdup_printf("http://%s:%d/", host, port);
-      gHttpProxy = httpproxy;
-    }
-
-    g_free(host);
-    g_free(httpproxy);
-
-    if (gconf_client_get_bool(conf, HTTP_PROXY_DIR "/use_authentication",
-                              nullptr)) {
-      gchar *user, *password, *auth = nullptr;
-
-      user = gconf_client_get_string(
-          conf, HTTP_PROXY_DIR "/authentication_user", nullptr);
-      password = gconf_client_get_string(
-          conf, HTTP_PROXY_DIR "/authentication_password", nullptr);
-
-      if (user && password) {
-        auth = g_strdup_printf("%s:%s", user, password);
-        gAuth = auth;
-      }
-
-      g_free(user);
-      g_free(password);
-      g_free(auth);
-    }
-  }
-
-  g_object_unref(conf);
-
-  // Don't dlclose gconfLib as libORBit-2 uses atexit().
-}
-
-gpointer SendThread(gpointer args) {
-  Json::StreamWriterBuilder builder;
-  builder["indentation"] = "";
-  string parameters(writeString(builder, gQueryParameters));
-
-  string response, error;
-  long response_code;
-
-  bool success = google_breakpad::HTTPUpload::SendRequest(
-      gSendURL, parameters, gFiles, gHttpProxy, gAuth, gCACertificateFile,
-      &response, &response_code, &error);
-  if (success) {
-    LogMessage("Crash report submitted successfully");
-  } else {
-    LogMessage("Crash report submission failed: " + error);
-  }
-
-  SendCompleted(success, response);
-
-  if (!gAutoSubmit) {
-    // Apparently glib is threadsafe, and will schedule this
-    // on the main thread, see:
-    // http://library.gnome.org/devel/gtk-faq/stable/x499.html
-    g_idle_add(ReportCompleted, (gpointer)success);
-  }
-
-  return nullptr;
-}
-
-gboolean WindowDeleted(GtkWidget* window, GdkEvent* event, gpointer userData) {
-  SaveSettings();
-  gtk_main_quit();
-  return TRUE;
-}
-
-gboolean check_escape(GtkWidget* window, GdkEventKey* event,
-                      gpointer userData) {
-  if (event->keyval == GDK_KEY_Escape) {
-    gtk_main_quit();
-    return TRUE;
-  }
-  return FALSE;
-}
-
-static void MaybeSubmitReport() {
-  if (gtk_toggle_button_get_active(GTK_TOGGLE_BUTTON(gSubmitReportCheck))) {
-    gDidTrySend = true;
-    DisableGUIAndSendReport();
-  } else {
-    gtk_main_quit();
-  }
-}
-
-void CloseClicked(GtkButton* button, gpointer userData) {
-  SaveSettings();
-  MaybeSubmitReport();
-}
-
-void RestartClicked(GtkButton* button, gpointer userData) {
-  SaveSettings();
-  RestartApplication();
-  MaybeSubmitReport();
-}
-
-static void UpdateURL() {
-  if (gtk_toggle_button_get_active(GTK_TOGGLE_BUTTON(gIncludeURLCheck))) {
-    gQueryParameters["URL"] = gURLParameter;
-  } else {
-    gQueryParameters.removeMember("URL");
-  }
-}
-
-void SubmitReportChecked(GtkButton* sender, gpointer userData) {
-  UpdateSubmit();
-}
-
-void IncludeURLClicked(GtkButton* sender, gpointer userData) { UpdateURL(); }
-
-/* === Crashreporter UI Functions === */
-
-bool UIInit() {
-  // breakpad probably left us with blocked signals, unblock them here
-  sigset_t signals, old;
-  sigfillset(&signals);
-  sigprocmask(SIG_UNBLOCK, &signals, &old);
-
-  // tell glib we're going to use threads
-  g_thread_init(nullptr);
-
-  if (gtk_init_check(&gArgc, &gArgv)) {
-    gInitialized = true;
-
-    if (gStrings.find("isRTL") != gStrings.end() && gStrings["isRTL"] == "yes")
-      gtk_widget_set_default_direction(GTK_TEXT_DIR_RTL);
-
-    return true;
-  }
-
-  return false;
-}
-
-void UIShowDefaultUI() {
-  GtkWidget* errorDialog = gtk_message_dialog_new(
-      nullptr, GTK_DIALOG_MODAL, GTK_MESSAGE_ERROR, GTK_BUTTONS_CLOSE, "%s",
-      gStrings[ST_CRASHREPORTERDEFAULT].c_str());
-
-  gtk_window_set_title(GTK_WINDOW(errorDialog),
-                       gStrings[ST_CRASHREPORTERTITLE].c_str());
-  gtk_dialog_run(GTK_DIALOG(errorDialog));
-}
-
-void UIError_impl(const string& message) {
-  if (!gInitialized) {
-    // Didn't initialize, this is the best we can do
-    printf("Error: %s\n", message.c_str());
-    return;
-  }
-
-  GtkWidget* errorDialog =
-      gtk_message_dialog_new(nullptr, GTK_DIALOG_MODAL, GTK_MESSAGE_ERROR,
-                             GTK_BUTTONS_CLOSE, "%s", message.c_str());
-
-  gtk_window_set_title(GTK_WINDOW(errorDialog),
-                       gStrings[ST_CRASHREPORTERTITLE].c_str());
-  gtk_dialog_run(GTK_DIALOG(errorDialog));
-}
-
-bool UIGetIniPath(string& path) {
-  path = gArgv[0];
-  path.append(".ini");
-
-  return true;
-}
-
-/*
- * Settings are stored in ~/.vendor/product, or
- * ~/.product if vendor is empty.
- */
-bool UIGetSettingsPath(const string& vendor, const string& product,
-                       string& settingsPath) {
-  char* home = getenv("HOME");
-
-  if (!home) return false;
-
-  settingsPath = home;
-  settingsPath += "/.";
-  if (!vendor.empty()) {
-    string lc_vendor;
-    std::transform(vendor.begin(), vendor.end(), back_inserter(lc_vendor),
-                   (int (*)(int))std::tolower);
-    settingsPath += lc_vendor + "/";
-  }
-  string lc_product;
-  std::transform(product.begin(), product.end(), back_inserter(lc_product),
-                 (int (*)(int))std::tolower);
-  settingsPath += lc_product + "/Crash Reports";
-  return true;
-}
-
-bool UIMoveFile(const string& file, const string& newfile) {
-  if (!rename(file.c_str(), newfile.c_str())) return true;
-  if (errno != EXDEV) return false;
-
-  // use system /bin/mv instead, time to fork
-  pid_t pID = vfork();
-  if (pID < 0) {
-    // Failed to fork
-    return false;
-  }
-  if (pID == 0) {
-    char* const args[4] = {const_cast<char*>("mv"), strdup(file.c_str()),
-                           strdup(newfile.c_str()), 0};
-    if (args[1] && args[2]) execve("/bin/mv", args, 0);
-    free(args[1]);
-    free(args[2]);
-    exit(-1);
-  }
-  int status;
-  waitpid(pID, &status, 0);
-  return UIFileExists(newfile);
-}
diff --git a/toolkit/crashreporter/client/crashreporter_gtk_common.h b/toolkit/crashreporter/client/crashreporter_gtk_common.h
deleted file mode 100644
index 208c7ba6b0..0000000000
--- a/toolkit/crashreporter/client/crashreporter_gtk_common.h
+++ /dev/null
@@ -1,50 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-#ifndef CRASHREPORTER_GTK_COMMON_H__
-#define CRASHREPORTER_GTK_COMMON_H__
-
-#include <glib.h>
-#include <gtk/gtk.h>
-
-#include <string>
-#include <vector>
-
-#include "json/json.h"
-
-const char kIniFile[] = "crashreporter.ini";
-
-extern GtkWidget* gWindow;
-extern GtkWidget* gSubmitReportCheck;
-extern GtkWidget* gIncludeURLCheck;
-extern GtkWidget* gThrobber;
-extern GtkWidget* gProgressLabel;
-extern GtkWidget* gCloseButton;
-extern GtkWidget* gRestartButton;
-
-extern std::vector<std::string> gRestartArgs;
-extern GThread* gSendThreadID;
-
-extern bool gInitialized;
-extern bool gDidTrySend;
-extern StringTable gFiles;
-extern Json::Value gQueryParameters;
-extern std::string gHttpProxy;
-extern std::string gAuth;
-extern std::string gCACertificateFile;
-extern std::string gSendURL;
-extern std::string gURLParameter;
-
-void LoadProxyinfo();
-gboolean CloseApp(gpointer data);
-gpointer SendThread(gpointer args);
-gboolean WindowDeleted(GtkWidget* window, GdkEvent* event, gpointer userData);
-gboolean check_escape(GtkWidget* window, GdkEventKey* event, gpointer data);
-void SubmitReportChecked(GtkButton* sender, gpointer userData);
-void IncludeURLClicked(GtkButton* sender, gpointer userData);
-void CloseClicked(GtkButton* button, gpointer userData);
-void RestartClicked(GtkButton* button, gpointer userData);
-void SaveSettings(void);
-
-#endif  // CRASHREPORTER_GTK_COMMON_H__
diff --git a/toolkit/crashreporter/client/crashreporter_linux.cpp b/toolkit/crashreporter/client/crashreporter_linux.cpp
deleted file mode 100644
index 644b34654e..0000000000
--- a/toolkit/crashreporter/client/crashreporter_linux.cpp
+++ /dev/null
@@ -1,525 +0,0 @@
-/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-#include <dlfcn.h>
-#include <fcntl.h>
-#include <glib.h>
-#include <gtk/gtk.h>
-#include <string.h>
-
-#include <cctype>
-
-#include "crashreporter.h"
-#include "crashreporter_gtk_common.h"
-
-#define LABEL_MAX_CHAR_WIDTH 48
-
-using std::ios;
-using std::string;
-using std::vector;
-
-using namespace CrashReporter;
-
-static GtkWidget* gViewReportButton = 0;
-static GtkWidget* gCommentTextLabel = 0;
-static GtkWidget* gCommentText = 0;
-
-static bool gCommentFieldHint = true;
-
-// handle from dlopen'ing libgnome
-static void* gnomeLib = nullptr;
-// handle from dlopen'ing libgnomeui
-static void* gnomeuiLib = nullptr;
-
-static void LoadSettings() {
-  /*
-   * NOTE! This code needs to stay in sync with the preference checking
-   *       code in in nsExceptionHandler.cpp.
-   */
-
-  bool includeURL = true;
-  bool submitReport = true;
-  StringTable settings;
-  if (ReadStringsFromFile(gSettingsPath + "/" + kIniFile, settings, true)) {
-    if (settings.find("IncludeURL") != settings.end()) {
-      includeURL = settings["IncludeURL"][0] != '0';
-    }
-    if (settings.find("SubmitReport") != settings.end()) {
-      submitReport = settings["SubmitReport"][0] != '0';
-    }
-  }
-
-  if (gIncludeURLCheck) {
-    gtk_toggle_button_set_active(GTK_TOGGLE_BUTTON(gIncludeURLCheck),
-                                 includeURL);
-  }
-  gtk_toggle_button_set_active(GTK_TOGGLE_BUTTON(gSubmitReportCheck),
-                               submitReport);
-}
-
-static string Escape(const string& str) {
-  string ret;
-  for (auto c : str) {
-    if (c == '\\') {
-      ret += "\\\\";
-    } else if (c == '\n') {
-      ret += "\\n";
-    } else if (c == '\t') {
-      ret += "\\t";
-    } else {
-      ret.push_back(c);
-    }
-  }
-
-  return ret;
-}
-
-static bool WriteStrings(std::ostream& out, const string& header,
-                         StringTable& strings, bool escape) {
-  out << "[" << header << "]\n";
-  for (const auto& iter : strings) {
-    out << iter.first << "=";
-    if (escape) {
-      out << Escape(iter.second);
-    } else {
-      out << iter.second;
-    }
-
-    out << '\n';
-  }
-
-  return true;
-}
-
-static bool WriteStringsToFile(const string& path, const string& header,
-                               StringTable& strings, bool escape) {
-  std::ofstream* f = UIOpenWrite(path, ios::trunc);
-  bool success = false;
-  if (f->is_open()) {
-    success = WriteStrings(*f, header, strings, escape);
-    f->close();
-  }
-
-  delete f;
-  return success;
-}
-
-void SaveSettings() {
-  /*
-   * NOTE! This code needs to stay in sync with the preference setting
-   *       code in in nsExceptionHandler.cpp.
-   */
-
-  StringTable settings;
-
-  ReadStringsFromFile(gSettingsPath + "/" + kIniFile, settings, true);
-  if (gIncludeURLCheck != 0)
-    settings["IncludeURL"] =
-        gtk_toggle_button_get_active(GTK_TOGGLE_BUTTON(gIncludeURLCheck)) ? "1"
-                                                                          : "0";
-  settings["SubmitReport"] =
-      gtk_toggle_button_get_active(GTK_TOGGLE_BUTTON(gSubmitReportCheck)) ? "1"
-                                                                          : "0";
-
-  WriteStringsToFile(gSettingsPath + "/" + kIniFile, "Crash Reporter", settings,
-                     true);
-}
-
-void SendReport() {
-  LoadProxyinfo();
-
-  // spawn a thread to do the sending
-  gSendThreadID = g_thread_create(SendThread, nullptr, TRUE, nullptr);
-}
-
-void DisableGUIAndSendReport() {
-  // disable all our gui controls, show the throbber + change the progress text
-  gtk_widget_set_sensitive(gSubmitReportCheck, FALSE);
-  gtk_widget_set_sensitive(gViewReportButton, FALSE);
-  gtk_widget_set_sensitive(gCommentText, FALSE);
-  if (gIncludeURLCheck) gtk_widget_set_sensitive(gIncludeURLCheck, FALSE);
-  gtk_widget_set_sensitive(gCloseButton, FALSE);
-  if (gRestartButton) gtk_widget_set_sensitive(gRestartButton, FALSE);
-  gtk_widget_show_all(gThrobber);
-  gtk_label_set_text(GTK_LABEL(gProgressLabel),
-                     gStrings[ST_REPORTDURINGSUBMIT].c_str());
-
-  SendReport();
-}
-
-static void ShowReportInfo(GtkTextView* viewReportTextView) {
-  GtkTextBuffer* buffer = gtk_text_view_get_buffer(viewReportTextView);
-
-  GtkTextIter start, end;
-  gtk_text_buffer_get_start_iter(buffer, &start);
-  gtk_text_buffer_get_end_iter(buffer, &end);
-
-  gtk_text_buffer_delete(buffer, &start, &end);
-
-  for (Json::ValueConstIterator iter = gQueryParameters.begin();
-       iter != gQueryParameters.end(); ++iter) {
-    gtk_text_buffer_insert(buffer, &end, iter.name().c_str(),
-                           iter.name().length());
-    gtk_text_buffer_insert(buffer, &end, ": ", -1);
-    string value;
-    if (iter->isString()) {
-      value = iter->asString();
-    } else {
-      Json::StreamWriterBuilder builder;
-      builder["indentation"] = "";
-      value = writeString(builder, *iter);
-    }
-    gtk_text_buffer_insert(buffer, &end, value.c_str(), value.length());
-    gtk_text_buffer_insert(buffer, &end, "\n", -1);
-  }
-
-  gtk_text_buffer_insert(buffer, &end, "\n", -1);
-  gtk_text_buffer_insert(buffer, &end, gStrings[ST_EXTRAREPORTINFO].c_str(),
-                         -1);
-}
-
-void UpdateSubmit() {
-  if (gtk_toggle_button_get_active(GTK_TOGGLE_BUTTON(gSubmitReportCheck))) {
-    gtk_widget_set_sensitive(gViewReportButton, TRUE);
-    gtk_widget_set_sensitive(gCommentText, TRUE);
-    if (gIncludeURLCheck) gtk_widget_set_sensitive(gIncludeURLCheck, TRUE);
-    gtk_label_set_text(GTK_LABEL(gProgressLabel),
-                       gStrings[ST_REPORTPRESUBMIT].c_str());
-  } else {
-    gtk_widget_set_sensitive(gViewReportButton, FALSE);
-    gtk_widget_set_sensitive(gCommentText, FALSE);
-    if (gIncludeURLCheck) gtk_widget_set_sensitive(gIncludeURLCheck, FALSE);
-    gtk_label_set_text(GTK_LABEL(gProgressLabel), "");
-  }
-}
-
-static void ViewReportClicked(GtkButton* button, gpointer userData) {
-  GtkDialog* dialog = GTK_DIALOG(gtk_dialog_new_with_buttons(
-      gStrings[ST_VIEWREPORTTITLE].c_str(), GTK_WINDOW(gWindow),
-      GTK_DIALOG_MODAL, GTK_STOCK_OK, GTK_RESPONSE_OK, nullptr));
-
-  GtkWidget* scrolled = gtk_scrolled_window_new(0, 0);
-  gtk_container_add(GTK_CONTAINER(gtk_dialog_get_content_area(dialog)),
-                    scrolled);
-  gtk_scrolled_window_set_policy(GTK_SCROLLED_WINDOW(scrolled),
-                                 GTK_POLICY_AUTOMATIC, GTK_POLICY_ALWAYS);
-  gtk_scrolled_window_set_shadow_type(GTK_SCROLLED_WINDOW(scrolled),
-                                      GTK_SHADOW_IN);
-  gtk_widget_set_vexpand(scrolled, TRUE);
-
-  GtkWidget* viewReportTextView = gtk_text_view_new();
-  gtk_container_add(GTK_CONTAINER(scrolled), viewReportTextView);
-  gtk_text_view_set_editable(GTK_TEXT_VIEW(viewReportTextView), FALSE);
-  gtk_text_view_set_wrap_mode(GTK_TEXT_VIEW(viewReportTextView), GTK_WRAP_WORD);
-  gtk_widget_set_size_request(GTK_WIDGET(viewReportTextView), -1, 100);
-
-  ShowReportInfo(GTK_TEXT_VIEW(viewReportTextView));
-
-  gtk_dialog_set_default_response(dialog, GTK_RESPONSE_OK);
-  gtk_widget_set_size_request(GTK_WIDGET(dialog), 400, 200);
-  gtk_widget_show_all(GTK_WIDGET(dialog));
-  gtk_dialog_run(dialog);
-  gtk_widget_destroy(GTK_WIDGET(dialog));
-}
-
-static void CommentChanged(GtkTextBuffer* buffer, gpointer userData) {
-  GtkTextIter start, end;
-  gtk_text_buffer_get_start_iter(buffer, &start);
-  gtk_text_buffer_get_end_iter(buffer, &end);
-  const char* comment = gtk_text_buffer_get_text(buffer, &start, &end, TRUE);
-  if (comment[0] == '\0' || gCommentFieldHint) {
-    gQueryParameters.removeMember("Comments");
-  } else {
-    gQueryParameters["Comments"] = comment;
-  }
-}
-
-static void CommentInsert(GtkTextBuffer* buffer, GtkTextIter* location,
-                          gchar* text, gint len, gpointer userData) {
-  GtkTextIter start, end;
-  gtk_text_buffer_get_start_iter(buffer, &start);
-  gtk_text_buffer_get_end_iter(buffer, &end);
-  const char* comment = gtk_text_buffer_get_text(buffer, &start, &end, TRUE);
-
-  // limit to 500 bytes in utf-8
-  if (strlen(comment) + len > MAX_COMMENT_LENGTH) {
-    g_signal_stop_emission_by_name(buffer, "insert-text");
-  }
-}
-
-static void UpdateHintText(GtkWidget* widget, gboolean gainedFocus,
-                           bool* hintShowing, const char* hintText) {
-  GtkTextBuffer* buffer = nullptr;
-  if (GTK_IS_TEXT_VIEW(widget))
-    buffer = gtk_text_view_get_buffer(GTK_TEXT_VIEW(widget));
-
-  if (gainedFocus) {
-    if (*hintShowing) {
-      if (buffer == nullptr) {  // sort of cheating
-        gtk_entry_set_text(GTK_ENTRY(widget), "");
-      } else {  // GtkTextView
-        gtk_text_buffer_set_text(buffer, "", 0);
-      }
-      gtk_widget_modify_text(widget, GTK_STATE_NORMAL, nullptr);
-      *hintShowing = false;
-    }
-  } else {
-    // lost focus
-    const char* text = nullptr;
-    if (buffer == nullptr) {
-      text = gtk_entry_get_text(GTK_ENTRY(widget));
-    } else {
-      GtkTextIter start, end;
-      gtk_text_buffer_get_start_iter(buffer, &start);
-      gtk_text_buffer_get_end_iter(buffer, &end);
-      text = gtk_text_buffer_get_text(buffer, &start, &end, TRUE);
-    }
-
-    if (text == nullptr || text[0] == '\0') {
-      *hintShowing = true;
-
-      if (buffer == nullptr) {
-        gtk_entry_set_text(GTK_ENTRY(widget), hintText);
-      } else {
-        gtk_text_buffer_set_text(buffer, hintText, -1);
-      }
-
-      gtk_widget_modify_text(
-          widget, GTK_STATE_NORMAL,
-          &gtk_widget_get_style(widget)->text[GTK_STATE_INSENSITIVE]);
-    }
-  }
-}
-
-static gboolean CommentFocusChange(GtkWidget* widget, GdkEventFocus* event,
-                                   gpointer userData) {
-  UpdateHintText(widget, event->in, &gCommentFieldHint,
-                 gStrings[ST_COMMENTGRAYTEXT].c_str());
-
-  return FALSE;
-}
-
-typedef struct _GnomeProgram GnomeProgram;
-typedef struct _GnomeModuleInfo GnomeModuleInfo;
-typedef GnomeProgram* (*_gnome_program_init_fn)(const char*, const char*,
-                                                const GnomeModuleInfo*, int,
-                                                char**, const char*, ...);
-typedef const GnomeModuleInfo* (*_libgnomeui_module_info_get_fn)();
-
-void TryInitGnome() {
-  gnomeLib = dlopen("libgnome-2.so.0", RTLD_LAZY);
-  if (!gnomeLib) return;
-
-  gnomeuiLib = dlopen("libgnomeui-2.so.0", RTLD_LAZY);
-  if (!gnomeuiLib) return;
-
-  _gnome_program_init_fn gnome_program_init =
-      (_gnome_program_init_fn)(dlsym(gnomeLib, "gnome_program_init"));
-  _libgnomeui_module_info_get_fn libgnomeui_module_info_get =
-      (_libgnomeui_module_info_get_fn)(dlsym(gnomeuiLib,
-                                             "libgnomeui_module_info_get"));
-
-  if (gnome_program_init && libgnomeui_module_info_get) {
-    gnome_program_init("crashreporter", "1.0", libgnomeui_module_info_get(),
-                       gArgc, gArgv, nullptr);
-  }
-}
-
-/* === Crashreporter UI Functions === */
-
-/*
- * Anything not listed here is in crashreporter_gtk_common.cpp:
- *  UIInit
- *  UIShowDefaultUI
- *  UIError_impl
- *  UIGetIniPath
- *  UIGetSettingsPath
- *  UIEnsurePathExists
- *  UIFileExists
- *  UIMoveFile
- *  UIDeleteFile
- *  UIOpenRead
- *  UIOpenWrite
- */
-
-void UIShutdown() {
-  if (gnomeuiLib) dlclose(gnomeuiLib);
-  // Don't dlclose gnomeLib as libgnomevfs and libORBit-2 use atexit().
-}
-
-bool UIShowCrashUI(const StringTable& files, const Json::Value& queryParameters,
-                   const string& sendURL, const vector<string>& restartArgs) {
-  gFiles = files;
-  gQueryParameters = queryParameters;
-  gSendURL = sendURL;
-  gRestartArgs = restartArgs;
-  if (gQueryParameters.isMember("URL")) {
-    gURLParameter = gQueryParameters["URL"].asString();
-  }
-
-  if (gAutoSubmit) {
-    SendReport();
-    CloseApp(nullptr);
-    return true;
-  }
-
-  gWindow = gtk_window_new(GTK_WINDOW_TOPLEVEL);
-  gtk_window_set_title(GTK_WINDOW(gWindow),
-                       gStrings[ST_CRASHREPORTERTITLE].c_str());
-  gtk_window_set_resizable(GTK_WINDOW(gWindow), FALSE);
-  gtk_window_set_position(GTK_WINDOW(gWindow), GTK_WIN_POS_CENTER);
-  gtk_container_set_border_width(GTK_CONTAINER(gWindow), 12);
-  g_signal_connect(gWindow, "delete-event", G_CALLBACK(WindowDeleted), 0);
-  g_signal_connect(gWindow, "key_press_event", G_CALLBACK(check_escape),
-                   nullptr);
-
-  GtkWidget* vbox = gtk_vbox_new(FALSE, 6);
-  gtk_container_add(GTK_CONTAINER(gWindow), vbox);
-
-  GtkWidget* titleLabel = gtk_label_new("");
-  gtk_box_pack_start(GTK_BOX(vbox), titleLabel, FALSE, FALSE, 0);
-  gtk_misc_set_alignment(GTK_MISC(titleLabel), 0, 0.5);
-  char* markup =
-      g_strdup_printf("<b>%s</b>", gStrings[ST_CRASHREPORTERHEADER].c_str());
-  gtk_label_set_markup(GTK_LABEL(titleLabel), markup);
-  g_free(markup);
-
-  GtkWidget* descriptionLabel =
-      gtk_label_new(gStrings[ST_CRASHREPORTERDESCRIPTION].c_str());
-  gtk_box_pack_start(GTK_BOX(vbox), descriptionLabel, TRUE, TRUE, 0);
-  // force the label to line wrap
-  gtk_label_set_max_width_chars(GTK_LABEL(descriptionLabel),
-                                LABEL_MAX_CHAR_WIDTH);
-  gtk_label_set_line_wrap(GTK_LABEL(descriptionLabel), TRUE);
-  gtk_label_set_selectable(GTK_LABEL(descriptionLabel), TRUE);
-  gtk_misc_set_alignment(GTK_MISC(descriptionLabel), 0, 0.5);
-
-  // this is honestly how they suggest you indent a section
-  GtkWidget* indentBox = gtk_hbox_new(FALSE, 0);
-  gtk_box_pack_start(GTK_BOX(vbox), indentBox, FALSE, FALSE, 0);
-  gtk_box_pack_start(GTK_BOX(indentBox), gtk_label_new(""), FALSE, FALSE, 6);
-
-  GtkWidget* innerVBox1 = gtk_vbox_new(FALSE, 0);
-  gtk_box_pack_start(GTK_BOX(indentBox), innerVBox1, TRUE, TRUE, 0);
-
-  gSubmitReportCheck =
-      gtk_check_button_new_with_label(gStrings[ST_CHECKSUBMIT].c_str());
-  gtk_box_pack_start(GTK_BOX(innerVBox1), gSubmitReportCheck, FALSE, FALSE, 0);
-  g_signal_connect(gSubmitReportCheck, "clicked",
-                   G_CALLBACK(SubmitReportChecked), 0);
-
-  // indent again, below the "submit report" checkbox
-  GtkWidget* indentBox2 = gtk_hbox_new(FALSE, 0);
-  gtk_box_pack_start(GTK_BOX(innerVBox1), indentBox2, FALSE, FALSE, 0);
-  gtk_box_pack_start(GTK_BOX(indentBox2), gtk_label_new(""), FALSE, FALSE, 6);
-
-  GtkWidget* innerVBox = gtk_vbox_new(FALSE, 0);
-  gtk_box_pack_start(GTK_BOX(indentBox2), innerVBox, TRUE, TRUE, 0);
-  gtk_box_set_spacing(GTK_BOX(innerVBox), 6);
-
-  GtkWidget* viewReportButtonBox = gtk_hbutton_box_new();
-  gtk_box_pack_start(GTK_BOX(innerVBox), viewReportButtonBox, FALSE, FALSE, 0);
-  gtk_box_set_spacing(GTK_BOX(viewReportButtonBox), 6);
-  gtk_button_box_set_layout(GTK_BUTTON_BOX(viewReportButtonBox),
-                            GTK_BUTTONBOX_START);
-
-  gViewReportButton =
-      gtk_button_new_with_label(gStrings[ST_VIEWREPORT].c_str());
-  gtk_box_pack_start(GTK_BOX(viewReportButtonBox), gViewReportButton, FALSE,
-                     FALSE, 0);
-  g_signal_connect(gViewReportButton, "clicked", G_CALLBACK(ViewReportClicked),
-                   0);
-
-  GtkWidget* scrolled = gtk_scrolled_window_new(0, 0);
-  gtk_container_add(GTK_CONTAINER(innerVBox), scrolled);
-  gtk_scrolled_window_set_policy(GTK_SCROLLED_WINDOW(scrolled),
-                                 GTK_POLICY_NEVER, GTK_POLICY_ALWAYS);
-  gtk_scrolled_window_set_shadow_type(GTK_SCROLLED_WINDOW(scrolled),
-                                      GTK_SHADOW_IN);
-  gtk_scrolled_window_set_min_content_height(GTK_SCROLLED_WINDOW(scrolled),
-                                             100);
-
-  gCommentTextLabel = gtk_label_new(gStrings[ST_COMMENTGRAYTEXT].c_str());
-  gCommentText = gtk_text_view_new();
-  gtk_label_set_mnemonic_widget(GTK_LABEL(gCommentTextLabel), gCommentText);
-  gtk_text_view_set_accepts_tab(GTK_TEXT_VIEW(gCommentText), FALSE);
-  g_signal_connect(gCommentText, "focus-in-event",
-                   G_CALLBACK(CommentFocusChange), 0);
-  g_signal_connect(gCommentText, "focus-out-event",
-                   G_CALLBACK(CommentFocusChange), 0);
-
-  GtkTextBuffer* commentBuffer =
-      gtk_text_view_get_buffer(GTK_TEXT_VIEW(gCommentText));
-  g_signal_connect(commentBuffer, "changed", G_CALLBACK(CommentChanged), 0);
-  g_signal_connect(commentBuffer, "insert-text", G_CALLBACK(CommentInsert), 0);
-
-  gtk_container_add(GTK_CONTAINER(scrolled), gCommentText);
-  gtk_text_view_set_wrap_mode(GTK_TEXT_VIEW(gCommentText), GTK_WRAP_WORD_CHAR);
-  gtk_widget_set_size_request(GTK_WIDGET(gCommentText), -1, 100);
-
-  if (gQueryParameters.isMember("URL")) {
-    gIncludeURLCheck =
-        gtk_check_button_new_with_label(gStrings[ST_CHECKURL].c_str());
-    gtk_box_pack_start(GTK_BOX(innerVBox), gIncludeURLCheck, FALSE, FALSE, 0);
-    g_signal_connect(gIncludeURLCheck, "clicked", G_CALLBACK(IncludeURLClicked),
-                     0);
-    // on by default
-    gtk_toggle_button_set_active(GTK_TOGGLE_BUTTON(gIncludeURLCheck), TRUE);
-  }
-
-  GtkWidget* progressBox = gtk_hbox_new(FALSE, 6);
-  gtk_box_pack_start(GTK_BOX(vbox), progressBox, TRUE, TRUE, 0);
-
-  // Get the throbber image from alongside the executable
-  char* dir = g_path_get_dirname(gArgv[0]);
-  char* path = g_build_filename(dir, "Throbber-small.gif", nullptr);
-  g_free(dir);
-  gThrobber = gtk_image_new_from_file(path);
-  gtk_box_pack_start(GTK_BOX(progressBox), gThrobber, FALSE, FALSE, 0);
-
-  gProgressLabel = gtk_label_new(gStrings[ST_REPORTPRESUBMIT].c_str());
-  gtk_box_pack_start(GTK_BOX(progressBox), gProgressLabel, TRUE, TRUE, 0);
-  // force the label to line wrap
-  gtk_label_set_max_width_chars(GTK_LABEL(gProgressLabel),
-                                LABEL_MAX_CHAR_WIDTH);
-  gtk_label_set_line_wrap(GTK_LABEL(gProgressLabel), TRUE);
-
-  GtkWidget* buttonBox = gtk_hbutton_box_new();
-  gtk_box_pack_end(GTK_BOX(vbox), buttonBox, FALSE, FALSE, 0);
-  gtk_box_set_spacing(GTK_BOX(buttonBox), 6);
-  gtk_button_box_set_layout(GTK_BUTTON_BOX(buttonBox), GTK_BUTTONBOX_END);
-
-  gCloseButton = gtk_button_new_with_label(gStrings[ST_QUIT].c_str());
-  gtk_box_pack_start(GTK_BOX(buttonBox), gCloseButton, FALSE, FALSE, 0);
-  gtk_widget_set_can_default(gCloseButton, TRUE);
-  g_signal_connect(gCloseButton, "clicked", G_CALLBACK(CloseClicked), 0);
-
-  gRestartButton = 0;
-  if (!restartArgs.empty()) {
-    gRestartButton = gtk_button_new_with_label(gStrings[ST_RESTART].c_str());
-    gtk_box_pack_start(GTK_BOX(buttonBox), gRestartButton, FALSE, FALSE, 0);
-    gtk_widget_set_can_default(gRestartButton, TRUE);
-    g_signal_connect(gRestartButton, "clicked", G_CALLBACK(RestartClicked), 0);
-  }
-
-  gtk_widget_grab_focus(gSubmitReportCheck);
-
-  gtk_widget_grab_default(gRestartButton ? gRestartButton : gCloseButton);
-
-  LoadSettings();
-
-  UpdateSubmit();
-
-  UpdateHintText(gCommentText, FALSE, &gCommentFieldHint,
-                 gStrings[ST_COMMENTGRAYTEXT].c_str());
-
-  gtk_widget_show_all(gWindow);
-  // stick this here to avoid the show_all above...
-  gtk_widget_hide(gThrobber);
-
-  gtk_main();
-
-  return gDidTrySend;
-}
diff --git a/toolkit/crashreporter/client/crashreporter_osx.h b/toolkit/crashreporter/client/crashreporter_osx.h
deleted file mode 100644
index d9aeddb4b0..0000000000
--- a/toolkit/crashreporter/client/crashreporter_osx.h
+++ /dev/null
@@ -1,108 +0,0 @@
-/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-#ifndef CRASHREPORTER_OSX_H__
-#define CRASHREPORTER_OSX_H__
-
-#include <Cocoa/Cocoa.h>
-#include "HTTPMultipartUpload.h"
-#include "crashreporter.h"
-#include "json/json.h"
-
-// Defined below
-@class TextViewWithPlaceHolder;
-
-@interface CrashReporterUI : NSObject {
-  IBOutlet NSWindow* mWindow;
-
-  /* Crash reporter view */
-  IBOutlet NSTextField* mHeaderLabel;
-  IBOutlet NSTextField* mDescriptionLabel;
-  IBOutlet NSButton* mViewReportButton;
-  IBOutlet NSScrollView* mCommentScrollView;
-  IBOutlet TextViewWithPlaceHolder* mCommentText;
-  IBOutlet NSButton* mSubmitReportButton;
-  IBOutlet NSButton* mIncludeURLButton;
-  IBOutlet NSButton* mEmailMeButton;
-  IBOutlet NSTextField* mEmailText;
-  IBOutlet NSButton* mCloseButton;
-  IBOutlet NSButton* mRestartButton;
-  IBOutlet NSProgressIndicator* mProgressIndicator;
-  IBOutlet NSTextField* mProgressText;
-
-  /* Error view */
-  IBOutlet NSView* mErrorView;
-  IBOutlet NSTextField* mErrorHeaderLabel;
-  IBOutlet NSTextField* mErrorLabel;
-  IBOutlet NSButton* mErrorCloseButton;
-
-  /* For "show info" alert */
-  IBOutlet NSWindow* mViewReportWindow;
-  IBOutlet NSTextView* mViewReportTextView;
-  IBOutlet NSButton* mViewReportOkButton;
-
-  HTTPMultipartUpload* mPost;
-}
-
-- (void)showCrashUI:(const StringTable&)files
-    queryParameters:(const Json::Value&)queryParameters
-            sendURL:(const std::string&)sendURL;
-- (void)showErrorUI:(const std::string&)message;
-- (void)showReportInfo;
-- (void)maybeSubmitReport;
-- (void)closeMeDown:(id)unused;
-
-- (IBAction)submitReportClicked:(id)sender;
-- (IBAction)viewReportClicked:(id)sender;
-- (IBAction)viewReportOkClicked:(id)sender;
-- (IBAction)closeClicked:(id)sender;
-- (IBAction)restartClicked:(id)sender;
-- (IBAction)includeURLClicked:(id)sender;
-
-- (void)textDidChange:(NSNotification*)aNotification;
-- (BOOL)textView:(NSTextView*)aTextView
-    shouldChangeTextInRange:(NSRange)affectedCharRange
-          replacementString:(NSString*)replacementString;
-
-- (void)doInitialResizing;
-- (float)setStringFitVertically:(NSControl*)control
-                         string:(NSString*)str
-                   resizeWindow:(BOOL)resizeWindow;
-- (void)setView:(NSView*)v animate:(BOOL)animate;
-- (void)enableControls:(BOOL)enabled;
-- (void)updateSubmit;
-- (void)updateURL;
-- (void)updateEmail;
-- (void)sendReport;
-- (bool)setupPost;
-- (void)uploadThread:(HTTPMultipartUpload*)post;
-- (void)uploadComplete:(NSData*)data;
-
-- (BOOL)applicationShouldTerminateAfterLastWindowClosed:
-    (NSApplication*)theApplication;
-- (void)applicationWillTerminate:(NSNotification*)aNotification;
-
-@end
-
-/*
- * Subclass NSTextView to provide a text view with placeholder text.
- * Also provide a setEnabled implementation.
- */
-@interface TextViewWithPlaceHolder : NSTextView {
-  NSMutableAttributedString* mPlaceHolderString;
-}
-
-- (BOOL)becomeFirstResponder;
-- (void)drawRect:(NSRect)rect;
-- (BOOL)resignFirstResponder;
-- (void)setPlaceholder:(NSString*)placeholder;
-- (void)insertTab:(id)sender;
-- (void)insertBacktab:(id)sender;
-- (void)setEnabled:(BOOL)enabled;
-- (void)dealloc;
-
-@end
-
-#endif
diff --git a/toolkit/crashreporter/client/crashreporter_osx.mm b/toolkit/crashreporter/client/crashreporter_osx.mm
deleted file mode 100644
index b6d5d8ac6f..0000000000
--- a/toolkit/crashreporter/client/crashreporter_osx.mm
+++ /dev/null
@@ -1,805 +0,0 @@
-/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-#import <Cocoa/Cocoa.h>
-#import <CoreFoundation/CoreFoundation.h>
-#include "crashreporter.h"
-#include "crashreporter_osx.h"
-#include <crt_externs.h>
-#include <spawn.h>
-#include <sys/stat.h>
-#include <sys/types.h>
-#include <fcntl.h>
-#include <sstream>
-
-using std::ostringstream;
-using std::string;
-using std::vector;
-
-using namespace CrashReporter;
-
-static NSAutoreleasePool* gMainPool;
-static CrashReporterUI* gUI = 0;
-static StringTable gFiles;
-static Json::Value gQueryParameters;
-static string gURLParameter;
-static string gSendURL;
-static vector<string> gRestartArgs;
-static bool gDidTrySend = false;
-static bool gRTLlayout = false;
-
-static cpu_type_t pref_cpu_types[2] = {
-#if defined(__i386__)
-    CPU_TYPE_X86,
-#elif defined(__x86_64__)
-    CPU_TYPE_X86_64,
-#elif defined(__ppc__)
-    CPU_TYPE_POWERPC,
-#elif defined(__aarch64__)
-    CPU_TYPE_ARM64,
-#endif
-    CPU_TYPE_ANY};
-
-#define NSSTR(s) [NSString stringWithUTF8String:(s).c_str()]
-
-static NSString* Str(const char* aName) {
-  string str = gStrings[aName];
-  if (str.empty()) str = "?";
-  return NSSTR(str);
-}
-
-static bool RestartApplication() {
-  vector<char*> argv(gRestartArgs.size() + 1);
-
-  posix_spawnattr_t spawnattr;
-  if (posix_spawnattr_init(&spawnattr) != 0) {
-    return false;
-  }
-
-  // Set spawn attributes.
-  size_t attr_count = sizeof(pref_cpu_types) / sizeof(pref_cpu_types[0]);
-  size_t attr_ocount = 0;
-  if (posix_spawnattr_setbinpref_np(&spawnattr, attr_count, pref_cpu_types,
-                                    &attr_ocount) != 0 ||
-      attr_ocount != attr_count) {
-    posix_spawnattr_destroy(&spawnattr);
-    return false;
-  }
-
-  unsigned int i;
-  for (i = 0; i < gRestartArgs.size(); i++) {
-    argv[i] = (char*)gRestartArgs[i].c_str();
-  }
-  argv[i] = 0;
-
-  char** env = NULL;
-  char*** nsEnv = _NSGetEnviron();
-  if (nsEnv) env = *nsEnv;
-  int result = posix_spawnp(NULL, argv[0], NULL, &spawnattr, &argv[0], env);
-
-  posix_spawnattr_destroy(&spawnattr);
-
-  return result == 0;
-}
-
-@implementation CrashReporterUI
-
-- (void)awakeFromNib {
-  gUI = self;
-  [mWindow center];
-
-  [mWindow setTitle:[[NSBundle mainBundle]
-                        objectForInfoDictionaryKey:@"CFBundleName"]];
-  [NSApp activateIgnoringOtherApps:YES];
-}
-
-- (void)showCrashUI:(const StringTable&)files
-    queryParameters:(const Json::Value&)queryParameters
-            sendURL:(const string&)sendURL {
-  gFiles = files;
-  gQueryParameters = queryParameters;
-  gSendURL = sendURL;
-
-  if (gAutoSubmit) {
-    gDidTrySend = true;
-    [self sendReport];
-    return;
-  }
-
-  [mWindow setTitle:Str(ST_CRASHREPORTERTITLE)];
-  [mHeaderLabel setStringValue:Str(ST_CRASHREPORTERHEADER)];
-
-  NSRect viewReportFrame = [mViewReportButton frame];
-  [mViewReportButton setTitle:Str(ST_VIEWREPORT)];
-  [mViewReportButton sizeToFit];
-  if (gRTLlayout) {
-    // sizeToFit will keep the left side fixed, so realign
-    float oldWidth = viewReportFrame.size.width;
-    viewReportFrame = [mViewReportButton frame];
-    viewReportFrame.origin.x += oldWidth - viewReportFrame.size.width;
-    [mViewReportButton setFrame:viewReportFrame];
-  }
-
-  [mSubmitReportButton setTitle:Str(ST_CHECKSUBMIT)];
-  [mIncludeURLButton setTitle:Str(ST_CHECKURL)];
-  [mViewReportOkButton setTitle:Str(ST_OK)];
-
-  [mCommentText setPlaceholder:Str(ST_COMMENTGRAYTEXT)];
-  if (gRTLlayout) [mCommentText toggleBaseWritingDirection:self];
-
-  if (gQueryParameters.isMember("URL")) {
-    // save the URL value in case the checkbox gets unchecked
-    gURLParameter = gQueryParameters["URL"].asString();
-  } else {
-    // no URL specified, hide checkbox
-    [mIncludeURLButton removeFromSuperview];
-    // shrink window to fit
-    NSRect frame = [mWindow frame];
-    NSRect includeURLFrame = [mIncludeURLButton frame];
-    NSRect emailFrame = [mEmailMeButton frame];
-    int buttonMask = [mViewReportButton autoresizingMask];
-    int checkMask = [mSubmitReportButton autoresizingMask];
-    int commentScrollMask = [mCommentScrollView autoresizingMask];
-
-    [mViewReportButton setAutoresizingMask:NSViewMinYMargin];
-    [mSubmitReportButton setAutoresizingMask:NSViewMinYMargin];
-    [mCommentScrollView setAutoresizingMask:NSViewMinYMargin];
-
-    // remove all the space in between
-    frame.size.height -= includeURLFrame.origin.y - emailFrame.origin.y;
-    [mWindow setFrame:frame display:true animate:NO];
-
-    [mViewReportButton setAutoresizingMask:buttonMask];
-    [mSubmitReportButton setAutoresizingMask:checkMask];
-    [mCommentScrollView setAutoresizingMask:commentScrollMask];
-  }
-
-  // resize some buttons horizontally and possibly some controls vertically
-  [self doInitialResizing];
-
-  // load default state of submit checkbox
-  // we don't just do this via IB because we want the default to be
-  // off a certain percentage of the time
-  BOOL submitChecked = YES;
-  NSUserDefaults* userDefaults = [NSUserDefaults standardUserDefaults];
-  if (nil != [userDefaults objectForKey:@"submitReport"]) {
-    submitChecked = [userDefaults boolForKey:@"submitReport"];
-  } else {
-    [userDefaults setBool:submitChecked forKey:@"submitReport"];
-  }
-  [mSubmitReportButton setState:(submitChecked ? NSOnState : NSOffState)];
-
-  // load default state of include URL checkbox
-  BOOL includeChecked = YES;
-  if (nil != [userDefaults objectForKey:@"IncludeURL"]) {
-    includeChecked = [userDefaults boolForKey:@"IncludeURL"];
-  } else {
-    [userDefaults setBool:includeChecked forKey:@"IncludeURL"];
-  }
-  [mIncludeURLButton setState:(includeChecked ? NSOnState : NSOffState)];
-
-  [self updateSubmit];
-  [self updateURL];
-  [self updateEmail];
-
-  [mWindow makeKeyAndOrderFront:nil];
-}
-
-- (void)showErrorUI:(const string&)message {
-  [self setView:mErrorView animate:NO];
-
-  [mErrorHeaderLabel setStringValue:Str(ST_CRASHREPORTERHEADER)];
-  [self setStringFitVertically:mErrorLabel
-                        string:NSSTR(message)
-                  resizeWindow:YES];
-  [mErrorCloseButton setTitle:Str(ST_OK)];
-
-  [mErrorCloseButton setKeyEquivalent:@"\r"];
-  [mWindow makeFirstResponder:mErrorCloseButton];
-  [mWindow makeKeyAndOrderFront:nil];
-}
-
-- (void)showReportInfo {
-  NSDictionary* boldAttr = @{
-    NSFontAttributeName :
-        [NSFont boldSystemFontOfSize:[NSFont smallSystemFontSize]],
-    NSForegroundColorAttributeName : NSColor.textColor,
-  };
-  NSDictionary* normalAttr = @{
-    NSFontAttributeName :
-        [NSFont systemFontOfSize:[NSFont smallSystemFontSize]],
-    NSForegroundColorAttributeName : NSColor.textColor,
-  };
-
-  [mViewReportTextView setString:@""];
-  for (Json::ValueConstIterator iter = gQueryParameters.begin();
-       iter != gQueryParameters.end(); ++iter) {
-    NSAttributedString* key =
-        [[NSAttributedString alloc] initWithString:NSSTR(iter.name() + ": ")
-                                        attributes:boldAttr];
-    string str;
-    if (iter->isString()) {
-      str = iter->asString();
-    } else {
-      Json::StreamWriterBuilder builder;
-      builder["indentation"] = "";
-      str = writeString(builder, *iter);
-    }
-    NSAttributedString* value =
-        [[NSAttributedString alloc] initWithString:NSSTR(str + "\n")
-                                        attributes:normalAttr];
-    [[mViewReportTextView textStorage] appendAttributedString:key];
-    [[mViewReportTextView textStorage] appendAttributedString:value];
-    [key release];
-    [value release];
-  }
-
-  NSAttributedString* extra = [[NSAttributedString alloc]
-      initWithString:NSSTR("\n" + gStrings[ST_EXTRAREPORTINFO])
-          attributes:normalAttr];
-  [[mViewReportTextView textStorage] appendAttributedString:extra];
-  [extra release];
-}
-
-- (void)maybeSubmitReport {
-  if ([mSubmitReportButton state] == NSOnState) {
-    [self setStringFitVertically:mProgressText
-                          string:Str(ST_REPORTDURINGSUBMIT)
-                    resizeWindow:YES];
-    // disable all the controls
-    [self enableControls:NO];
-    [mSubmitReportButton setEnabled:NO];
-    [mRestartButton setEnabled:NO];
-    [mCloseButton setEnabled:NO];
-    [mProgressIndicator startAnimation:self];
-    gDidTrySend = true;
-    [self sendReport];
-  } else {
-    [NSApp terminate:self];
-  }
-}
-
-- (void)closeMeDown:(id)unused {
-  [NSApp terminate:self];
-}
-
-- (IBAction)submitReportClicked:(id)sender {
-  [self updateSubmit];
-  NSUserDefaults* userDefaults = [NSUserDefaults standardUserDefaults];
-  [userDefaults setBool:([mSubmitReportButton state] == NSOnState)
-                 forKey:@"submitReport"];
-  [userDefaults synchronize];
-}
-
-- (IBAction)viewReportClicked:(id)sender {
-  [self showReportInfo];
-  [NSApp beginSheet:mViewReportWindow
-      modalForWindow:mWindow
-       modalDelegate:nil
-      didEndSelector:nil
-         contextInfo:nil];
-}
-
-- (IBAction)viewReportOkClicked:(id)sender {
-  [mViewReportWindow orderOut:nil];
-  [NSApp endSheet:mViewReportWindow];
-}
-
-- (IBAction)closeClicked:(id)sender {
-  [self maybeSubmitReport];
-}
-
-- (IBAction)restartClicked:(id)sender {
-  RestartApplication();
-  [self maybeSubmitReport];
-}
-
-- (IBAction)includeURLClicked:(id)sender {
-  [self updateURL];
-  NSUserDefaults* userDefaults = [NSUserDefaults standardUserDefaults];
-  [userDefaults setBool:([mIncludeURLButton state] == NSOnState)
-                 forKey:@"IncludeURL"];
-  [userDefaults synchronize];
-}
-
-- (void)textDidChange:(NSNotification*)aNotification {
-  // update comment parameter
-  if ([[[mCommentText textStorage] mutableString] length] > 0)
-    gQueryParameters["Comments"] =
-        [[[mCommentText textStorage] mutableString] UTF8String];
-  else
-    gQueryParameters.removeMember("Comments");
-}
-
-// Limit the comment field to 500 bytes in UTF-8
-- (BOOL)textView:(NSTextView*)aTextView
-    shouldChangeTextInRange:(NSRange)affectedCharRange
-          replacementString:(NSString*)replacementString {
-  // current string length + replacement text length - replaced range length
-  if (([[aTextView string] lengthOfBytesUsingEncoding:NSUTF8StringEncoding] +
-       [replacementString lengthOfBytesUsingEncoding:NSUTF8StringEncoding] -
-       [[[aTextView string] substringWithRange:affectedCharRange]
-           lengthOfBytesUsingEncoding:NSUTF8StringEncoding]) >
-      MAX_COMMENT_LENGTH) {
-    return NO;
-  }
-  return YES;
-}
-
-- (void)doInitialResizing {
-  NSRect windowFrame = [mWindow frame];
-  NSRect restartFrame = [mRestartButton frame];
-  NSRect closeFrame = [mCloseButton frame];
-  // resize close button to fit text
-  float oldCloseWidth = closeFrame.size.width;
-  [mCloseButton setTitle:Str(ST_QUIT)];
-  [mCloseButton sizeToFit];
-  closeFrame = [mCloseButton frame];
-  // move close button left if it grew
-  if (!gRTLlayout) {
-    closeFrame.origin.x -= closeFrame.size.width - oldCloseWidth;
-  }
-
-  if (gRestartArgs.size() == 0) {
-    [mRestartButton removeFromSuperview];
-    if (!gRTLlayout) {
-      closeFrame.origin.x = restartFrame.origin.x +
-                            (restartFrame.size.width - closeFrame.size.width);
-    } else {
-      closeFrame.origin.x = restartFrame.origin.x;
-    }
-    [mCloseButton setFrame:closeFrame];
-    [mCloseButton setKeyEquivalent:@"\r"];
-  } else {
-    [mRestartButton setTitle:Str(ST_RESTART)];
-    // resize "restart" button
-    float oldRestartWidth = restartFrame.size.width;
-    [mRestartButton sizeToFit];
-    restartFrame = [mRestartButton frame];
-    if (!gRTLlayout) {
-      // move left by the amount that the button grew
-      restartFrame.origin.x -= restartFrame.size.width - oldRestartWidth;
-      closeFrame.origin.x -= restartFrame.size.width - oldRestartWidth;
-    } else {
-      // shift the close button right in RTL
-      closeFrame.origin.x += restartFrame.size.width - oldRestartWidth;
-    }
-    [mRestartButton setFrame:restartFrame];
-    [mCloseButton setFrame:closeFrame];
-    // possibly resize window if both buttons no longer fit
-    // leave 20 px from either side of the window, and 12 px
-    // between the buttons
-    float neededWidth =
-        closeFrame.size.width + restartFrame.size.width + 2 * 20 + 12;
-
-    if (neededWidth > windowFrame.size.width) {
-      windowFrame.size.width = neededWidth;
-      [mWindow setFrame:windowFrame display:true animate:NO];
-    }
-    [mRestartButton setKeyEquivalent:@"\r"];
-  }
-
-  NSButton* checkboxes[] = {mSubmitReportButton, mIncludeURLButton};
-
-  for (auto checkbox : checkboxes) {
-    NSRect frame = [checkbox frame];
-    [checkbox sizeToFit];
-    if (gRTLlayout) {
-      // sizeToFit will keep the left side fixed, so realign
-      float oldWidth = frame.size.width;
-      frame = [checkbox frame];
-      frame.origin.x += oldWidth - frame.size.width;
-      [checkbox setFrame:frame];
-    }
-    // keep existing spacing on left side, + 20 px spare on right
-    float neededWidth =
-        frame.origin.x + checkbox.intrinsicContentSize.width + 20;
-    if (neededWidth > windowFrame.size.width) {
-      windowFrame.size.width = neededWidth;
-      [mWindow setFrame:windowFrame display:true animate:NO];
-    }
-  }
-
-  // do this down here because we may have made the window wider
-  // up above
-  [self setStringFitVertically:mDescriptionLabel
-                        string:Str(ST_CRASHREPORTERDESCRIPTION)
-                  resizeWindow:YES];
-
-  // now pin all the controls (except quit/submit) in place,
-  // if we lengthen the window after this, it's just to lengthen
-  // the progress text, so nothing above that text should move.
-  NSView* views[] = {mSubmitReportButton, mViewReportButton,
-                     mCommentScrollView,  mIncludeURLButton,
-                     mProgressIndicator,  mProgressText};
-  for (auto view : views) {
-    [view setAutoresizingMask:NSViewMinYMargin];
-  }
-}
-
-- (float)setStringFitVertically:(NSControl*)control
-                         string:(NSString*)str
-                   resizeWindow:(BOOL)resizeWindow {
-  // hack to make the text field grow vertically
-  NSRect frame = [control frame];
-  float oldHeight = frame.size.height;
-
-  frame.size.height = 10000;
-  NSSize oldCellSize = [[control cell] cellSizeForBounds:frame];
-  [control setStringValue:str];
-  NSSize newCellSize = [[control cell] cellSizeForBounds:frame];
-
-  float delta = newCellSize.height - oldCellSize.height;
-  frame.origin.y -= delta;
-  frame.size.height = oldHeight + delta;
-  [control setFrame:frame];
-
-  if (resizeWindow) {
-    NSRect frame = [mWindow frame];
-    frame.origin.y -= delta;
-    frame.size.height += delta;
-    [mWindow setFrame:frame display:true animate:NO];
-  }
-
-  return delta;
-}
-
-- (void)setView:(NSView*)v animate:(BOOL)animate {
-  NSRect frame = [mWindow frame];
-
-  NSRect oldViewFrame = [[mWindow contentView] frame];
-  NSRect newViewFrame = [v frame];
-
-  frame.origin.y += oldViewFrame.size.height - newViewFrame.size.height;
-  frame.size.height -= oldViewFrame.size.height - newViewFrame.size.height;
-
-  frame.origin.x += oldViewFrame.size.width - newViewFrame.size.width;
-  frame.size.width -= oldViewFrame.size.width - newViewFrame.size.width;
-
-  [mWindow setContentView:v];
-  [mWindow setFrame:frame display:true animate:animate];
-}
-
-- (void)enableControls:(BOOL)enabled {
-  [mViewReportButton setEnabled:enabled];
-  [mIncludeURLButton setEnabled:enabled];
-  [mCommentText setEnabled:enabled];
-  [mCommentScrollView setHasVerticalScroller:enabled];
-}
-
-- (void)updateSubmit {
-  if ([mSubmitReportButton state] == NSOnState) {
-    [self setStringFitVertically:mProgressText
-                          string:Str(ST_REPORTPRESUBMIT)
-                    resizeWindow:YES];
-    [mProgressText setHidden:NO];
-    // enable all the controls
-    [self enableControls:YES];
-  } else {
-    // not submitting, disable all the controls under
-    // the submit checkbox, and hide the status text
-    [mProgressText setHidden:YES];
-    [self enableControls:NO];
-  }
-}
-
-- (void)updateURL {
-  if ([mIncludeURLButton state] == NSOnState && !gURLParameter.empty()) {
-    gQueryParameters["URL"] = gURLParameter;
-  } else {
-    gQueryParameters.removeMember("URL");
-  }
-}
-
-- (void)updateEmail {
-  // In order to remove the email fields, we have to edit the .nib files which
-  // we can't do with current xcode so we make them hidden; updating the
-  // crashreporter interface for mac is covered in bug #1696164
-  [mEmailMeButton setHidden:YES];
-  [mEmailText setHidden:YES];
-}
-
-- (void)sendReport {
-  if (![self setupPost]) {
-    LogMessage("Crash report submission failed: could not set up POST data");
-
-    if (gAutoSubmit) {
-      [NSApp terminate:self];
-    }
-
-    [self setStringFitVertically:mProgressText
-                          string:Str(ST_SUBMITFAILED)
-                    resizeWindow:YES];
-    // quit after 5 seconds
-    [self performSelector:@selector(closeMeDown:)
-               withObject:nil
-               afterDelay:5.0];
-  }
-
-  [NSThread detachNewThreadSelector:@selector(uploadThread:)
-                           toTarget:self
-                         withObject:mPost];
-}
-
-- (bool)setupPost {
-  NSURL* url = [NSURL
-      URLWithString:[NSSTR(gSendURL) stringByAddingPercentEscapesUsingEncoding:
-                                         NSUTF8StringEncoding]];
-  if (!url) return false;
-
-  mPost = [[HTTPMultipartUpload alloc] initWithURL:url];
-  if (!mPost) return false;
-
-  for (StringTable::const_iterator i = gFiles.begin(); i != gFiles.end(); i++) {
-    [mPost addFileAtPath:NSSTR(i->second) name:NSSTR(i->first)];
-  }
-
-  Json::StreamWriterBuilder builder;
-  builder["indentation"] = "";
-  string output = writeString(builder, gQueryParameters).append("\r\n");
-  NSMutableString* parameters =
-      [[NSMutableString alloc] initWithUTF8String:output.c_str()];
-
-  [mPost setParameters:parameters];
-  [parameters release];
-
-  return true;
-}
-
-- (void)uploadComplete:(NSData*)data {
-  NSHTTPURLResponse* response = [mPost response];
-  [mPost release];
-
-  bool success;
-  string reply;
-  if (!data || !response || [response statusCode] != 200) {
-    success = false;
-    reply = "";
-
-    // if data is nil, we probably logged an error in uploadThread
-    if (data != nil && response != nil) {
-      ostringstream message;
-      message << "Crash report submission failed: server returned status "
-              << [response statusCode];
-      LogMessage(message.str());
-    }
-  } else {
-    success = true;
-    LogMessage("Crash report submitted successfully");
-
-    NSString* encodingName = [response textEncodingName];
-    NSStringEncoding encoding;
-    if (encodingName) {
-      encoding = CFStringConvertEncodingToNSStringEncoding(
-          CFStringConvertIANACharSetNameToEncoding((CFStringRef)encodingName));
-    } else {
-      encoding = NSISOLatin1StringEncoding;
-    }
-    NSString* r = [[NSString alloc] initWithData:data encoding:encoding];
-    reply = [r UTF8String];
-    [r release];
-  }
-
-  SendCompleted(success, reply);
-
-  if (gAutoSubmit) {
-    [NSApp terminate:self];
-  }
-
-  [mProgressIndicator stopAnimation:self];
-  if (success) {
-    [self setStringFitVertically:mProgressText
-                          string:Str(ST_REPORTSUBMITSUCCESS)
-                    resizeWindow:YES];
-  } else {
-    [self setStringFitVertically:mProgressText
-                          string:Str(ST_SUBMITFAILED)
-                    resizeWindow:YES];
-  }
-  // quit after 5 seconds
-  [self performSelector:@selector(closeMeDown:) withObject:nil afterDelay:5.0];
-}
-
-- (void)uploadThread:(HTTPMultipartUpload*)post {
-  NSAutoreleasePool* autoreleasepool = [[NSAutoreleasePool alloc] init];
-  NSError* error = nil;
-  NSData* data = [post send:&error];
-  if (error) {
-    data = nil;
-    NSString* errorDesc = [error localizedDescription];
-    string message = [errorDesc UTF8String];
-    LogMessage("Crash report submission failed: " + message);
-  }
-
-  [self performSelectorOnMainThread:@selector(uploadComplete:)
-                         withObject:data
-                      waitUntilDone:YES];
-
-  [autoreleasepool release];
-}
-
-// to get auto-quit when we close the window
-- (BOOL)applicationShouldTerminateAfterLastWindowClosed:
-    (NSApplication*)theApplication {
-  return YES;
-}
-
-- (void)applicationWillTerminate:(NSNotification*)aNotification {
-  // since we use [NSApp terminate:] we never return to main,
-  // so do our cleanup here
-  if (!gDidTrySend) DeleteDump();
-}
-
-@end
-
-@implementation TextViewWithPlaceHolder
-
-- (BOOL)becomeFirstResponder {
-  [self setNeedsDisplay:YES];
-  return [super becomeFirstResponder];
-}
-
-- (void)drawRect:(NSRect)rect {
-  [super drawRect:rect];
-  if (mPlaceHolderString && [[self string] isEqualToString:@""] &&
-      self != [[self window] firstResponder])
-    [mPlaceHolderString drawInRect:[self frame]];
-}
-
-- (BOOL)resignFirstResponder {
-  [self setNeedsDisplay:YES];
-  return [super resignFirstResponder];
-}
-
-- (void)setPlaceholder:(NSString*)placeholder {
-  NSColor* txtColor = [NSColor disabledControlTextColor];
-  NSDictionary* txtDict = [NSDictionary
-      dictionaryWithObjectsAndKeys:txtColor, NSForegroundColorAttributeName,
-                                   nil];
-  mPlaceHolderString =
-      [[NSMutableAttributedString alloc] initWithString:placeholder
-                                             attributes:txtDict];
-  if (gRTLlayout)
-    [mPlaceHolderString setAlignment:NSTextAlignmentRight
-                               range:NSMakeRange(0, [placeholder length])];
-}
-
-- (void)insertTab:(id)sender {
-  // don't actually want to insert tabs, just tab to next control
-  [[self window] selectNextKeyView:sender];
-}
-
-- (void)insertBacktab:(id)sender {
-  [[self window] selectPreviousKeyView:sender];
-}
-
-- (void)setEnabled:(BOOL)enabled {
-  [self setSelectable:enabled];
-  [self setEditable:enabled];
-  if (![[self string] isEqualToString:@""]) {
-    NSAttributedString* colorString;
-    NSColor* txtColor;
-    if (enabled)
-      txtColor = [NSColor textColor];
-    else
-      txtColor = [NSColor disabledControlTextColor];
-    NSDictionary* txtDict = [NSDictionary
-        dictionaryWithObjectsAndKeys:txtColor, NSForegroundColorAttributeName,
-                                     nil];
-    colorString = [[NSAttributedString alloc] initWithString:[self string]
-                                                  attributes:txtDict];
-    [[self textStorage] setAttributedString:colorString];
-    [self setInsertionPointColor:txtColor];
-    [colorString release];
-  }
-}
-
-- (void)dealloc {
-  [mPlaceHolderString release];
-  [super dealloc];
-}
-
-@end
-
-/* === Crashreporter UI Functions === */
-
-bool UIInit() {
-  gMainPool = [[NSAutoreleasePool alloc] init];
-  [NSApplication sharedApplication];
-
-  if (gStrings.find("isRTL") != gStrings.end() && gStrings["isRTL"] == "yes")
-    gRTLlayout = true;
-
-  if (gAutoSubmit) {
-    gUI = [[CrashReporterUI alloc] init];
-  } else {
-    [[NSBundle mainBundle]
-           loadNibNamed:(gRTLlayout ? @"MainMenuRTL" : @"MainMenu")
-                  owner:NSApp
-        topLevelObjects:nil];
-  }
-
-  return true;
-}
-
-void UIShutdown() { [gMainPool release]; }
-
-void UIShowDefaultUI() {
-  [gUI showErrorUI:gStrings[ST_CRASHREPORTERDEFAULT]];
-  [NSApp run];
-}
-
-bool UIShowCrashUI(const StringTable& files, const Json::Value& queryParameters,
-                   const string& sendURL, const vector<string>& restartArgs) {
-  gRestartArgs = restartArgs;
-
-  [gUI showCrashUI:files queryParameters:queryParameters sendURL:sendURL];
-  [NSApp run];
-
-  return gDidTrySend;
-}
-
-void UIError_impl(const string& message) {
-  if (!gUI) {
-    // UI failed to initialize, printing is the best we can do
-    printf("Error: %s\n", message.c_str());
-    return;
-  }
-
-  [gUI showErrorUI:message];
-  [NSApp run];
-}
-
-bool UIGetIniPath(string& path) {
-  NSString* tmpPath = [NSString stringWithUTF8String:gArgv[0]];
-  NSString* iniName = [tmpPath lastPathComponent];
-  iniName = [iniName stringByAppendingPathExtension:@"ini"];
-  tmpPath = [tmpPath stringByDeletingLastPathComponent];
-  tmpPath = [tmpPath stringByDeletingLastPathComponent];
-  tmpPath = [tmpPath stringByAppendingPathComponent:@"Resources"];
-  tmpPath = [tmpPath stringByAppendingPathComponent:iniName];
-  path = [tmpPath UTF8String];
-  return true;
-}
-
-bool UIGetSettingsPath(const string& vendor, const string& product,
-                       string& settingsPath) {
-  NSArray* paths = NSSearchPathForDirectoriesInDomains(
-      NSApplicationSupportDirectory, NSUserDomainMask, YES);
-  NSString* destPath = [paths firstObject];
-
-  // Note that MacOS ignores the vendor when creating the profile hierarchy -
-  // all application preferences directories live alongside one another in
-  // ~/Library/Application Support/
-  destPath = [destPath stringByAppendingPathComponent:NSSTR(product)];
-  // Thunderbird stores its profile in ~/Library/Thunderbird,
-  // but we're going to put stuff in ~/Library/Application Support/Thunderbird
-  // anyway, so we have to ensure that path exists.
-  string tempPath = [destPath UTF8String];
-  if (!UIEnsurePathExists(tempPath)) return false;
-
-  destPath = [destPath stringByAppendingPathComponent:@"Crash Reports"];
-
-  settingsPath = [destPath UTF8String];
-
-  return true;
-}
-
-bool UIMoveFile(const string& file, const string& newfile) {
-  if (!rename(file.c_str(), newfile.c_str())) return true;
-  if (errno != EXDEV) return false;
-
-  NSFileManager* fileManager = [NSFileManager defaultManager];
-  NSString* source =
-      [fileManager stringWithFileSystemRepresentation:file.c_str()
-                                               length:file.length()];
-  NSString* dest =
-      [fileManager stringWithFileSystemRepresentation:newfile.c_str()
-                                               length:newfile.length()];
-  if (!source || !dest) return false;
-
-  [fileManager moveItemAtPath:source toPath:dest error:NULL];
-  return UIFileExists(newfile);
-}
diff --git a/toolkit/crashreporter/client/crashreporter_unix_common.cpp b/toolkit/crashreporter/client/crashreporter_unix_common.cpp
deleted file mode 100644
index e6514d4423..0000000000
--- a/toolkit/crashreporter/client/crashreporter_unix_common.cpp
+++ /dev/null
@@ -1,139 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-#include "crashreporter.h"
-
-#include <algorithm>
-#include <sys/wait.h>
-
-#include <dirent.h>
-#include <errno.h>
-#include <sys/stat.h>
-#include <unistd.h>
-
-using namespace CrashReporter;
-using std::ios_base;
-using std::sort;
-using std::string;
-using std::vector;
-
-struct FileData {
-  time_t timestamp;
-  string path;
-};
-
-static bool CompareFDTime(const FileData& fd1, const FileData& fd2) {
-  return fd1.timestamp > fd2.timestamp;
-}
-
-void UIPruneSavedDumps(const string& directory) {
-  DIR* dirfd = opendir(directory.c_str());
-  if (!dirfd) return;
-
-  vector<FileData> dumpfiles;
-
-  while (dirent* dir = readdir(dirfd)) {
-    FileData fd;
-    fd.path = directory + '/' + dir->d_name;
-    if (fd.path.size() < 5) continue;
-
-    if (fd.path.compare(fd.path.size() - 4, 4, ".dmp") != 0) continue;
-
-    struct stat st;
-    if (stat(fd.path.c_str(), &st)) {
-      closedir(dirfd);
-      return;
-    }
-
-    fd.timestamp = st.st_mtime;
-
-    dumpfiles.push_back(fd);
-  }
-
-  closedir(dirfd);
-
-  sort(dumpfiles.begin(), dumpfiles.end(), CompareFDTime);
-
-  while (dumpfiles.size() > kSaveCount) {
-    // get the path of the oldest file
-    string path = dumpfiles[dumpfiles.size() - 1].path;
-    UIDeleteFile(path);
-
-    // s/.dmp/.extra/
-    path.replace(path.size() - 4, 4, ".extra");
-    UIDeleteFile(path);
-
-    dumpfiles.pop_back();
-  }
-}
-
-bool UIRunProgram(const string& exename, const vector<string>& args,
-                  bool wait) {
-  pid_t pid = fork();
-
-  if (pid == -1) {
-    return false;
-  } else if (pid == 0) {
-    // Child
-    size_t argvLen = args.size() + 2;
-    vector<char*> argv(argvLen);
-
-    argv[0] = const_cast<char*>(exename.c_str());
-
-    for (size_t i = 0; i < args.size(); i++) {
-      argv[i + 1] = const_cast<char*>(args[i].c_str());
-    }
-
-    argv[argvLen - 1] = nullptr;
-
-    // Run the program
-    int rv = execv(exename.c_str(), argv.data());
-
-    if (rv == -1) {
-      exit(EXIT_FAILURE);
-    }
-  } else {
-    // Parent
-    if (wait) {
-      waitpid(pid, nullptr, 0);
-    }
-  }
-
-  return true;
-}
-
-bool UIEnsurePathExists(const string& path) {
-  int ret = mkdir(path.c_str(), S_IRWXU);
-  int e = errno;
-  if (ret == -1 && e != EEXIST) return false;
-
-  return true;
-}
-
-bool UIFileExists(const string& path) {
-  struct stat sb;
-  int ret = stat(path.c_str(), &sb);
-  if (ret == -1 || !(sb.st_mode & S_IFREG)) return false;
-
-  return true;
-}
-
-bool UIDeleteFile(const string& file) { return (unlink(file.c_str()) != -1); }
-
-std::ifstream* UIOpenRead(const string& filename, ios_base::openmode mode) {
-  return new std::ifstream(filename.c_str(), mode);
-}
-
-std::ofstream* UIOpenWrite(const string& filename, ios_base::openmode mode) {
-  return new std::ofstream(filename.c_str(), mode);
-}
-
-string UIGetEnv(const string& name) {
-  const char* var = getenv(name.c_str());
-  if (var && *var) {
-    return var;
-  }
-
-  return "";
-}
diff --git a/toolkit/crashreporter/client/crashreporter_win.cpp b/toolkit/crashreporter/client/crashreporter_win.cpp
deleted file mode 100644
index 35018bda4a..0000000000
--- a/toolkit/crashreporter/client/crashreporter_win.cpp
+++ /dev/null
@@ -1,1266 +0,0 @@
-/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-#ifdef WIN32_LEAN_AND_MEAN
-#  undef WIN32_LEAN_AND_MEAN
-#endif
-
-#include "crashreporter.h"
-
-#include <windows.h>
-#include <commctrl.h>
-#include <richedit.h>
-#include <shellapi.h>
-#include <shlobj.h>
-#include <shlwapi.h>
-#include <math.h>
-#include <set>
-#include <algorithm>
-#include "resource.h"
-#include "windows/sender/crash_report_sender.h"
-#include "common/windows/string_utils-inl.h"
-
-#define SUBMIT_REPORT_VALUE L"SubmitCrashReport"
-#define INCLUDE_URL_VALUE L"IncludeURL"
-
-#define WM_UPLOADCOMPLETE WM_APP
-
-// Thanks, Windows.h :(
-#undef min
-#undef max
-
-using std::ifstream;
-using std::ios;
-using std::ios_base;
-using std::map;
-using std::ofstream;
-using std::set;
-using std::string;
-using std::vector;
-using std::wstring;
-
-using namespace CrashReporter;
-
-typedef struct {
-  HWND hDlg;
-  Json::Value queryParameters;
-  map<wstring, wstring> files;
-  wstring sendURL;
-
-  wstring serverResponse;
-} SendThreadData;
-
-/*
- * Per http://msdn2.microsoft.com/en-us/library/ms645398(VS.85).aspx
- * "The DLGTEMPLATEEX structure is not defined in any standard header file.
- * The structure definition is provided here to explain the format of an
- * extended template for a dialog box.
- */
-typedef struct {
-  WORD dlgVer;
-  WORD signature;
-  DWORD helpID;
-  DWORD exStyle;
-  // There's more to this struct, but it has weird variable-length
-  // members, and I only actually need to touch exStyle on an existing
-  // instance, so I've omitted the rest.
-} DLGTEMPLATEEX;
-
-static HANDLE gThreadHandle;
-static SendThreadData gSendData = {
-    0,
-};
-static vector<string> gRestartArgs;
-static Json::Value gQueryParameters;
-static wstring gCrashReporterKey(L"Software\\Mozilla\\Crash Reporter");
-static string gURLParameter;
-static int gCheckboxPadding = 6;
-static bool gRTLlayout = false;
-
-// When vertically resizing the dialog, these items should move down
-static set<UINT> gAttachedBottom;
-
-// Default set of items for gAttachedBottom
-static const UINT kDefaultAttachedBottom[] = {
-    IDC_SUBMITREPORTCHECK, IDC_VIEWREPORTBUTTON, IDC_COMMENTTEXT,
-    IDC_INCLUDEURLCHECK,   IDC_PROGRESSTEXT,     IDC_THROBBER,
-    IDC_CLOSEBUTTON,       IDC_RESTARTBUTTON,
-};
-
-static wstring UTF8ToWide(const string& utf8, bool* success = 0);
-static DWORD WINAPI SendThreadProc(LPVOID param);
-
-static wstring Str(const char* key) { return UTF8ToWide(gStrings[key]); }
-
-/* === win32 helper functions === */
-
-static void DoInitCommonControls() {
-  INITCOMMONCONTROLSEX ic;
-  ic.dwSize = sizeof(INITCOMMONCONTROLSEX);
-  ic.dwICC = ICC_PROGRESS_CLASS;
-  InitCommonControlsEx(&ic);
-  // also get the rich edit control
-  LoadLibrary(L"Msftedit.dll");
-}
-
-static bool GetBoolValue(HKEY hRegKey, LPCTSTR valueName, DWORD* value) {
-  DWORD type, dataSize;
-  dataSize = sizeof(DWORD);
-  if (RegQueryValueEx(hRegKey, valueName, nullptr, &type, (LPBYTE)value,
-                      &dataSize) == ERROR_SUCCESS &&
-      type == REG_DWORD)
-    return true;
-
-  return false;
-}
-
-static bool CheckBoolKey(const wchar_t* key, const wchar_t* valueName,
-                         bool* enabled) {
-  /*
-   * NOTE! This code needs to stay in sync with the preference checking
-   *       code in in nsExceptionHandler.cpp.
-   */
-  *enabled = false;
-  bool found = false;
-  HKEY hRegKey;
-  DWORD val;
-  // see if our reg key is set globally
-  if (RegOpenKey(HKEY_LOCAL_MACHINE, key, &hRegKey) == ERROR_SUCCESS) {
-    if (GetBoolValue(hRegKey, valueName, &val)) {
-      *enabled = (val == 1);
-      found = true;
-    }
-    RegCloseKey(hRegKey);
-  } else {
-    // look for it in user settings
-    if (RegOpenKey(HKEY_CURRENT_USER, key, &hRegKey) == ERROR_SUCCESS) {
-      if (GetBoolValue(hRegKey, valueName, &val)) {
-        *enabled = (val == 1);
-        found = true;
-      }
-      RegCloseKey(hRegKey);
-    }
-  }
-
-  return found;
-}
-
-static void SetBoolKey(const wchar_t* key, const wchar_t* value, bool enabled) {
-  /*
-   * NOTE! This code needs to stay in sync with the preference setting
-   *       code in in nsExceptionHandler.cpp.
-   */
-  HKEY hRegKey;
-
-  if (RegCreateKey(HKEY_CURRENT_USER, key, &hRegKey) == ERROR_SUCCESS) {
-    DWORD data = (enabled ? 1 : 0);
-    RegSetValueEx(hRegKey, value, 0, REG_DWORD, (LPBYTE)&data, sizeof(data));
-    RegCloseKey(hRegKey);
-  }
-}
-
-static string FormatLastError() {
-  DWORD err = GetLastError();
-  LPWSTR s;
-  string message = "Crash report submission failed: ";
-  // odds are it's a WinInet error
-  HANDLE hInetModule = GetModuleHandle(L"WinInet.dll");
-  if (FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER |
-                        FORMAT_MESSAGE_FROM_SYSTEM |
-                        FORMAT_MESSAGE_FROM_HMODULE,
-                    hInetModule, err, 0, (LPWSTR)&s, 0, nullptr) != 0) {
-    message += WideToUTF8(s, nullptr);
-    LocalFree(s);
-    // strip off any trailing newlines
-    string::size_type n = message.find_last_not_of("\r\n");
-    if (n < message.size() - 1) {
-      message.erase(n + 1);
-    }
-  } else {
-    char buf[64];
-    sprintf(buf, "Unknown error, error code: 0x%08x",
-            static_cast<unsigned int>(err));
-    message += buf;
-  }
-  return message;
-}
-
-#define TS_DRAW 2
-#define BP_CHECKBOX 3
-
-typedef HANDLE(WINAPI* OpenThemeDataPtr)(HWND hwnd, LPCWSTR pszClassList);
-typedef HRESULT(WINAPI* CloseThemeDataPtr)(HANDLE hTheme);
-typedef HRESULT(WINAPI* GetThemePartSizePtr)(HANDLE hTheme, HDC hdc,
-                                             int iPartId, int iStateId,
-                                             RECT* prc, int ts, SIZE* psz);
-typedef HRESULT(WINAPI* GetThemeContentRectPtr)(HANDLE hTheme, HDC hdc,
-                                                int iPartId, int iStateId,
-                                                const RECT* pRect,
-                                                RECT* pContentRect);
-
-static void GetThemeSizes(HWND hwnd) {
-  HMODULE themeDLL = LoadLibrary(L"uxtheme.dll");
-
-  if (!themeDLL) return;
-
-  OpenThemeDataPtr openTheme =
-      (OpenThemeDataPtr)GetProcAddress(themeDLL, "OpenThemeData");
-  CloseThemeDataPtr closeTheme =
-      (CloseThemeDataPtr)GetProcAddress(themeDLL, "CloseThemeData");
-  GetThemePartSizePtr getThemePartSize =
-      (GetThemePartSizePtr)GetProcAddress(themeDLL, "GetThemePartSize");
-
-  if (!openTheme || !closeTheme || !getThemePartSize) {
-    FreeLibrary(themeDLL);
-    return;
-  }
-
-  HANDLE buttonTheme = openTheme(hwnd, L"Button");
-  if (!buttonTheme) {
-    FreeLibrary(themeDLL);
-    return;
-  }
-  HDC hdc = GetDC(hwnd);
-  SIZE s;
-  getThemePartSize(buttonTheme, hdc, BP_CHECKBOX, 0, nullptr, TS_DRAW, &s);
-  gCheckboxPadding = s.cx;
-  closeTheme(buttonTheme);
-  FreeLibrary(themeDLL);
-}
-
-// Gets the position of a window relative to another window's client area
-static void GetRelativeRect(HWND hwnd, HWND hwndParent, RECT* r) {
-  GetWindowRect(hwnd, r);
-  MapWindowPoints(nullptr, hwndParent, (POINT*)r, 2);
-}
-
-static void SetDlgItemVisible(HWND hwndDlg, UINT item, bool visible) {
-  HWND hwnd = GetDlgItem(hwndDlg, item);
-
-  ShowWindow(hwnd, visible ? SW_SHOW : SW_HIDE);
-}
-
-/* === Crash Reporting Dialog === */
-
-static void StretchDialog(HWND hwndDlg, int ydiff) {
-  RECT r;
-  GetWindowRect(hwndDlg, &r);
-  r.bottom += ydiff;
-  MoveWindow(hwndDlg, r.left, r.top, r.right - r.left, r.bottom - r.top, TRUE);
-}
-
-static void ReflowDialog(HWND hwndDlg, int ydiff) {
-  // Move items attached to the bottom down/up by as much as
-  // the window resize
-  for (set<UINT>::const_iterator item = gAttachedBottom.begin();
-       item != gAttachedBottom.end(); item++) {
-    RECT r;
-    HWND hwnd = GetDlgItem(hwndDlg, *item);
-    GetRelativeRect(hwnd, hwndDlg, &r);
-    r.top += ydiff;
-    r.bottom += ydiff;
-    MoveWindow(hwnd, r.left, r.top, r.right - r.left, r.bottom - r.top, TRUE);
-  }
-}
-
-static DWORD WINAPI SendThreadProc(LPVOID param) {
-  bool finishedOk;
-  SendThreadData* td = (SendThreadData*)param;
-
-  if (td->sendURL.empty()) {
-    finishedOk = false;
-    LogMessage("No server URL, not sending report");
-  } else {
-    Json::StreamWriterBuilder builder;
-    builder["indentation"] = "";
-    string parameters(Json::writeString(builder, td->queryParameters));
-    google_breakpad::CrashReportSender sender(L"");
-    finishedOk = (sender.SendCrashReport(td->sendURL, parameters, td->files,
-                                         &td->serverResponse) ==
-                  google_breakpad::RESULT_SUCCEEDED);
-    if (finishedOk) {
-      LogMessage("Crash report submitted successfully");
-    } else {
-      // get an error string and print it to the log
-      // XXX: would be nice to get the HTTP status code here, filed:
-      // http://code.google.com/p/google-breakpad/issues/detail?id=220
-      LogMessage(FormatLastError());
-    }
-  }
-
-  if (gAutoSubmit) {
-    // Ordinarily this is done on the main thread in CrashReporterDialogProc,
-    // for auto submit we don't run that and it should be safe to finish up
-    // here as is done on other platforms.
-    SendCompleted(finishedOk, WideToUTF8(gSendData.serverResponse));
-  } else {
-    PostMessage(td->hDlg, WM_UPLOADCOMPLETE, finishedOk ? 1 : 0, 0);
-  }
-
-  return 0;
-}
-
-static void EndCrashReporterDialog(HWND hwndDlg, int code) {
-  // Save the current values to the registry
-  SetBoolKey(gCrashReporterKey.c_str(), INCLUDE_URL_VALUE,
-             IsDlgButtonChecked(hwndDlg, IDC_INCLUDEURLCHECK) != 0);
-  SetBoolKey(gCrashReporterKey.c_str(), SUBMIT_REPORT_VALUE,
-             IsDlgButtonChecked(hwndDlg, IDC_SUBMITREPORTCHECK) != 0);
-
-  EndDialog(hwndDlg, code);
-}
-
-static void MaybeResizeProgressText(HWND hwndDlg) {
-  HWND hwndProgress = GetDlgItem(hwndDlg, IDC_PROGRESSTEXT);
-  HDC hdc = GetDC(hwndProgress);
-  HFONT hfont = (HFONT)SendMessage(hwndProgress, WM_GETFONT, 0, 0);
-  if (hfont) SelectObject(hdc, hfont);
-  SIZE size;
-  RECT rect;
-  GetRelativeRect(hwndProgress, hwndDlg, &rect);
-
-  wchar_t text[1024];
-  GetWindowText(hwndProgress, text, 1024);
-
-  if (!GetTextExtentPoint32(hdc, text, wcslen(text), &size)) return;
-
-  if (size.cx < (rect.right - rect.left)) return;
-
-  // Figure out how much we need to resize things vertically
-  // This is sort of a fudge, but it should be good enough.
-  int wantedHeight =
-      size.cy * (int)ceil((float)size.cx / (float)(rect.right - rect.left));
-  int diff = wantedHeight - (rect.bottom - rect.top);
-  if (diff <= 0) return;
-
-  MoveWindow(hwndProgress, rect.left, rect.top, rect.right - rect.left,
-             wantedHeight, TRUE);
-
-  gAttachedBottom.clear();
-  gAttachedBottom.insert(IDC_CLOSEBUTTON);
-  gAttachedBottom.insert(IDC_RESTARTBUTTON);
-
-  StretchDialog(hwndDlg, diff);
-
-  for (size_t i = 0; i < sizeof(kDefaultAttachedBottom) / sizeof(UINT); i++) {
-    gAttachedBottom.insert(kDefaultAttachedBottom[i]);
-  }
-}
-
-static void MaybeSendReport(HWND hwndDlg) {
-  if (!IsDlgButtonChecked(hwndDlg, IDC_SUBMITREPORTCHECK)) {
-    EndCrashReporterDialog(hwndDlg, 0);
-    return;
-  }
-
-  // disable all the form controls
-  EnableWindow(GetDlgItem(hwndDlg, IDC_SUBMITREPORTCHECK), false);
-  EnableWindow(GetDlgItem(hwndDlg, IDC_VIEWREPORTBUTTON), false);
-  EnableWindow(GetDlgItem(hwndDlg, IDC_COMMENTTEXT), false);
-  EnableWindow(GetDlgItem(hwndDlg, IDC_INCLUDEURLCHECK), false);
-  EnableWindow(GetDlgItem(hwndDlg, IDC_CLOSEBUTTON), false);
-  EnableWindow(GetDlgItem(hwndDlg, IDC_RESTARTBUTTON), false);
-
-  SetDlgItemText(hwndDlg, IDC_PROGRESSTEXT, Str(ST_REPORTDURINGSUBMIT).c_str());
-  MaybeResizeProgressText(hwndDlg);
-  // start throbber
-  // play entire AVI, and loop
-  Animate_Play(GetDlgItem(hwndDlg, IDC_THROBBER), 0, -1, -1);
-  SetDlgItemVisible(hwndDlg, IDC_THROBBER, true);
-  gThreadHandle = nullptr;
-  gSendData.hDlg = hwndDlg;
-  gSendData.queryParameters = gQueryParameters;
-
-  gThreadHandle =
-      CreateThread(nullptr, 0, SendThreadProc, &gSendData, 0, nullptr);
-}
-
-static void RestartApplication() {
-  wstring cmdLine;
-
-  for (unsigned int i = 0; i < gRestartArgs.size(); i++) {
-    cmdLine += L"\"" + UTF8ToWide(gRestartArgs[i]) + L"\" ";
-  }
-
-  STARTUPINFO si;
-  PROCESS_INFORMATION pi;
-
-  ZeroMemory(&si, sizeof(si));
-  si.cb = sizeof(si);
-  si.dwFlags = STARTF_USESHOWWINDOW;
-  si.wShowWindow = SW_SHOWNORMAL;
-  ZeroMemory(&pi, sizeof(pi));
-
-  if (CreateProcess(nullptr, (LPWSTR)cmdLine.c_str(), nullptr, nullptr, FALSE,
-                    0, nullptr, nullptr, &si, &pi)) {
-    CloseHandle(pi.hProcess);
-    CloseHandle(pi.hThread);
-  }
-}
-
-static void ShowReportInfo(HWND hwndDlg) {
-  wstring description;
-
-  for (Json::ValueConstIterator iter = gQueryParameters.begin();
-       iter != gQueryParameters.end(); ++iter) {
-    description += UTF8ToWide(iter.name());
-    description += L": ";
-    string value;
-    if (iter->isString()) {
-      value = iter->asString();
-    } else {
-      Json::StreamWriterBuilder builder;
-      builder["indentation"] = "";
-      value = Json::writeString(builder, *iter);
-    }
-    description += UTF8ToWide(value);
-    description += L"\n";
-  }
-
-  description += L"\n";
-  description += Str(ST_EXTRAREPORTINFO);
-
-  SetDlgItemText(hwndDlg, IDC_VIEWREPORTTEXT, description.c_str());
-}
-
-static void UpdateURL(HWND hwndDlg) {
-  if (IsDlgButtonChecked(hwndDlg, IDC_INCLUDEURLCHECK)) {
-    gQueryParameters["URL"] = gURLParameter;
-  } else {
-    gQueryParameters.removeMember("URL");
-  }
-}
-
-static void UpdateComment(HWND hwndDlg) {
-  wchar_t comment[MAX_COMMENT_LENGTH + 1];
-  GetDlgItemTextW(hwndDlg, IDC_COMMENTTEXT, comment,
-                  sizeof(comment) / sizeof(comment[0]));
-  if (wcslen(comment) > 0)
-    gQueryParameters["Comments"] = WideToUTF8(comment);
-  else
-    gQueryParameters.removeMember("Comments");
-}
-
-/*
- * Dialog procedure for the "view report" dialog.
- */
-static BOOL CALLBACK ViewReportDialogProc(HWND hwndDlg, UINT message,
-                                          WPARAM wParam, LPARAM lParam) {
-  switch (message) {
-    case WM_INITDIALOG: {
-      SetWindowText(hwndDlg, Str(ST_VIEWREPORTTITLE).c_str());
-      SetDlgItemText(hwndDlg, IDOK, Str(ST_OK).c_str());
-      SendDlgItemMessage(hwndDlg, IDC_VIEWREPORTTEXT, EM_SETTARGETDEVICE,
-                         (WPARAM) nullptr, 0);
-      ShowReportInfo(hwndDlg);
-      SetFocus(GetDlgItem(hwndDlg, IDOK));
-      return FALSE;
-    }
-
-    case WM_COMMAND: {
-      if (HIWORD(wParam) == BN_CLICKED && LOWORD(wParam) == IDOK)
-        EndDialog(hwndDlg, 0);
-      return FALSE;
-    }
-  }
-  return FALSE;
-}
-
-// Return the number of bytes this string will take encoded
-// in UTF-8
-static inline int BytesInUTF8(wchar_t* str) {
-  // Just count size of buffer for UTF-8, minus one
-  // (we don't need to count the null terminator)
-  return WideCharToMultiByte(CP_UTF8, 0, str, -1, nullptr, 0, nullptr,
-                             nullptr) -
-         1;
-}
-
-// Calculate the length of the text in this edit control (in bytes,
-// in the UTF-8 encoding) after replacing the current selection
-// with |insert|.
-static int NewTextLength(HWND hwndEdit, wchar_t* insert) {
-  wchar_t current[MAX_COMMENT_LENGTH + 1];
-
-  GetWindowText(hwndEdit, current, MAX_COMMENT_LENGTH + 1);
-  DWORD selStart, selEnd;
-  SendMessage(hwndEdit, EM_GETSEL, (WPARAM)&selStart, (LPARAM)&selEnd);
-
-  int selectionLength = 0;
-  if (selEnd - selStart > 0) {
-    wchar_t selection[MAX_COMMENT_LENGTH + 1];
-    google_breakpad::WindowsStringUtils::safe_wcsncpy(
-        selection, MAX_COMMENT_LENGTH + 1, current + selStart,
-        selEnd - selStart);
-    selection[selEnd - selStart] = '\0';
-    selectionLength = BytesInUTF8(selection);
-  }
-
-  // current string length + replacement text length
-  // - replaced selection length
-  return BytesInUTF8(current) + BytesInUTF8(insert) - selectionLength;
-}
-
-// Window procedure for subclassing edit controls
-static LRESULT CALLBACK EditSubclassProc(HWND hwnd, UINT uMsg, WPARAM wParam,
-                                         LPARAM lParam) {
-  static WNDPROC super = nullptr;
-
-  if (super == nullptr) super = (WNDPROC)GetWindowLongPtr(hwnd, GWLP_USERDATA);
-
-  switch (uMsg) {
-    case WM_PAINT: {
-      HDC hdc;
-      PAINTSTRUCT ps;
-      RECT r;
-      wchar_t windowText[1024];
-
-      GetWindowText(hwnd, windowText, 1024);
-      // if the control contains text or is focused, draw it normally
-      if (GetFocus() == hwnd || windowText[0] != '\0')
-        return CallWindowProc(super, hwnd, uMsg, wParam, lParam);
-
-      GetClientRect(hwnd, &r);
-      hdc = BeginPaint(hwnd, &ps);
-      FillRect(hdc, &r,
-               GetSysColorBrush(IsWindowEnabled(hwnd) ? COLOR_WINDOW
-                                                      : COLOR_BTNFACE));
-      SetTextColor(hdc, GetSysColor(COLOR_GRAYTEXT));
-      SelectObject(hdc, (HFONT)GetStockObject(DEFAULT_GUI_FONT));
-      SetBkMode(hdc, TRANSPARENT);
-      wchar_t* txt = (wchar_t*)GetProp(hwnd, L"PROP_GRAYTEXT");
-      // Get the actual edit control rect
-      CallWindowProc(super, hwnd, EM_GETRECT, 0, (LPARAM)&r);
-      UINT format = DT_EDITCONTROL | DT_NOPREFIX | DT_WORDBREAK | DT_INTERNAL;
-      if (gRTLlayout) format |= DT_RIGHT;
-      if (txt) DrawText(hdc, txt, wcslen(txt), &r, format);
-      EndPaint(hwnd, &ps);
-      return 0;
-    }
-
-      // We handle WM_CHAR and WM_PASTE to limit the comment box to 500
-      // bytes in UTF-8.
-    case WM_CHAR: {
-      // Leave accelerator keys and non-printing chars (except LF) alone
-      if (wParam & (1 << 24) || wParam & (1 << 29) ||
-          (wParam < ' ' && wParam != '\n'))
-        break;
-
-      wchar_t ch[2] = {(wchar_t)wParam, 0};
-      if (NewTextLength(hwnd, ch) > MAX_COMMENT_LENGTH) return 0;
-
-      break;
-    }
-
-    case WM_PASTE: {
-      if (IsClipboardFormatAvailable(CF_UNICODETEXT) && OpenClipboard(hwnd)) {
-        HGLOBAL hg = GetClipboardData(CF_UNICODETEXT);
-        wchar_t* pastedText = (wchar_t*)GlobalLock(hg);
-        int newSize = 0;
-
-        if (pastedText) newSize = NewTextLength(hwnd, pastedText);
-
-        GlobalUnlock(hg);
-        CloseClipboard();
-
-        if (newSize > MAX_COMMENT_LENGTH) return 0;
-      }
-      break;
-    }
-
-    case WM_SETFOCUS:
-    case WM_KILLFOCUS: {
-      RECT r;
-      GetClientRect(hwnd, &r);
-      InvalidateRect(hwnd, &r, TRUE);
-      break;
-    }
-
-    case WM_DESTROY: {
-      // cleanup our property
-      HGLOBAL hData = RemoveProp(hwnd, L"PROP_GRAYTEXT");
-      if (hData) GlobalFree(hData);
-    }
-  }
-
-  return CallWindowProc(super, hwnd, uMsg, wParam, lParam);
-}
-
-// Resize a control to fit this text
-static int ResizeControl(HWND hwndButton, RECT& rect, wstring text,
-                         bool shiftLeft, int userDefinedPadding) {
-  HDC hdc = GetDC(hwndButton);
-  HFONT hfont = (HFONT)SendMessage(hwndButton, WM_GETFONT, 0, 0);
-  if (hfont) SelectObject(hdc, hfont);
-  SIZE size, oldSize;
-  int sizeDiff = 0;
-
-  wchar_t oldText[1024];
-  GetWindowText(hwndButton, oldText, 1024);
-
-  if (GetTextExtentPoint32(hdc, text.c_str(), text.length(), &size)
-      // default text on the button
-      && GetTextExtentPoint32(hdc, oldText, wcslen(oldText), &oldSize)) {
-    /*
-     Expand control widths to accomidate wider text strings. For most
-     controls (including buttons) the text padding is defined by the
-     dialog's rc file. Some controls (such as checkboxes) have padding
-     that extends to the end of the dialog, in which case we ignore the
-     rc padding and rely on a user defined value passed in through
-     userDefinedPadding.
-    */
-    int textIncrease = size.cx - oldSize.cx;
-    if (textIncrease < 0) return 0;
-    int existingTextPadding;
-    if (userDefinedPadding == 0)
-      existingTextPadding = (rect.right - rect.left) - oldSize.cx;
-    else
-      existingTextPadding = userDefinedPadding;
-    sizeDiff = textIncrease + existingTextPadding;
-
-    if (shiftLeft) {
-      // shift left by the amount the button should grow
-      rect.left -= sizeDiff;
-    } else {
-      // grow right instead
-      rect.right += sizeDiff;
-    }
-    MoveWindow(hwndButton, rect.left, rect.top, rect.right - rect.left,
-               rect.bottom - rect.top, TRUE);
-  }
-  return sizeDiff;
-}
-
-// The window was resized horizontally, so widen some of our
-// controls to make use of the space
-static void StretchControlsToFit(HWND hwndDlg) {
-  int controls[] = {IDC_DESCRIPTIONTEXT, IDC_SUBMITREPORTCHECK, IDC_COMMENTTEXT,
-                    IDC_INCLUDEURLCHECK, IDC_PROGRESSTEXT};
-
-  RECT dlgRect;
-  GetClientRect(hwndDlg, &dlgRect);
-
-  for (size_t i = 0; i < sizeof(controls) / sizeof(controls[0]); i++) {
-    RECT r;
-    HWND hwndControl = GetDlgItem(hwndDlg, controls[i]);
-    GetRelativeRect(hwndControl, hwndDlg, &r);
-    // 6 pixel spacing on the right
-    if (r.right + 6 != dlgRect.right) {
-      r.right = dlgRect.right - 6;
-      MoveWindow(hwndControl, r.left, r.top, r.right - r.left, r.bottom - r.top,
-                 TRUE);
-    }
-  }
-}
-
-static void SubmitReportChecked(HWND hwndDlg) {
-  bool enabled = (IsDlgButtonChecked(hwndDlg, IDC_SUBMITREPORTCHECK) != 0);
-  EnableWindow(GetDlgItem(hwndDlg, IDC_VIEWREPORTBUTTON), enabled);
-  EnableWindow(GetDlgItem(hwndDlg, IDC_COMMENTTEXT), enabled);
-  EnableWindow(GetDlgItem(hwndDlg, IDC_INCLUDEURLCHECK), enabled);
-  SetDlgItemVisible(hwndDlg, IDC_PROGRESSTEXT, enabled);
-}
-
-static INT_PTR DialogBoxParamMaybeRTL(UINT idd, HWND hwndParent,
-                                      DLGPROC dlgProc, LPARAM param) {
-  INT_PTR rv = 0;
-  if (gRTLlayout) {
-    // We need to toggle the WS_EX_LAYOUTRTL style flag on the dialog
-    // template.
-    HRSRC hDialogRC = FindResource(nullptr, MAKEINTRESOURCE(idd), RT_DIALOG);
-    HGLOBAL hDlgTemplate = LoadResource(nullptr, hDialogRC);
-    DLGTEMPLATEEX* pDlgTemplate = (DLGTEMPLATEEX*)LockResource(hDlgTemplate);
-    unsigned long sizeDlg = SizeofResource(nullptr, hDialogRC);
-    HGLOBAL hMyDlgTemplate = GlobalAlloc(GPTR, sizeDlg);
-    DLGTEMPLATEEX* pMyDlgTemplate = (DLGTEMPLATEEX*)GlobalLock(hMyDlgTemplate);
-    memcpy(pMyDlgTemplate, pDlgTemplate, sizeDlg);
-
-    pMyDlgTemplate->exStyle |= WS_EX_LAYOUTRTL;
-
-    rv = DialogBoxIndirectParam(nullptr, (LPCDLGTEMPLATE)pMyDlgTemplate,
-                                hwndParent, dlgProc, param);
-    GlobalUnlock(hMyDlgTemplate);
-    GlobalFree(hMyDlgTemplate);
-  } else {
-    rv = DialogBoxParam(nullptr, MAKEINTRESOURCE(idd), hwndParent, dlgProc,
-                        param);
-  }
-
-  return rv;
-}
-
-static BOOL CALLBACK CrashReporterDialogProc(HWND hwndDlg, UINT message,
-                                             WPARAM wParam, LPARAM lParam) {
-  static int sHeight = 0;
-
-  bool success;
-  bool enabled;
-
-  switch (message) {
-    case WM_INITDIALOG: {
-      GetThemeSizes(hwndDlg);
-      RECT r;
-      GetClientRect(hwndDlg, &r);
-      sHeight = r.bottom - r.top;
-
-      SetWindowText(hwndDlg, Str(ST_CRASHREPORTERTITLE).c_str());
-      HICON hIcon =
-          LoadIcon(GetModuleHandle(nullptr), MAKEINTRESOURCE(IDI_MAINICON));
-      SendMessage(hwndDlg, WM_SETICON, ICON_SMALL, (LPARAM)hIcon);
-      SendMessage(hwndDlg, WM_SETICON, ICON_BIG, (LPARAM)hIcon);
-
-      // resize the "View Report" button based on the string length
-      RECT rect;
-      HWND hwnd = GetDlgItem(hwndDlg, IDC_VIEWREPORTBUTTON);
-      GetRelativeRect(hwnd, hwndDlg, &rect);
-      ResizeControl(hwnd, rect, Str(ST_VIEWREPORT), false, 0);
-      SetDlgItemText(hwndDlg, IDC_VIEWREPORTBUTTON, Str(ST_VIEWREPORT).c_str());
-
-      hwnd = GetDlgItem(hwndDlg, IDC_SUBMITREPORTCHECK);
-      GetRelativeRect(hwnd, hwndDlg, &rect);
-      long maxdiff = ResizeControl(hwnd, rect, Str(ST_CHECKSUBMIT), false,
-                                   gCheckboxPadding);
-      SetDlgItemText(hwndDlg, IDC_SUBMITREPORTCHECK,
-                     Str(ST_CHECKSUBMIT).c_str());
-
-      if (!CheckBoolKey(gCrashReporterKey.c_str(), SUBMIT_REPORT_VALUE,
-                        &enabled))
-        enabled = true;
-
-      CheckDlgButton(hwndDlg, IDC_SUBMITREPORTCHECK,
-                     enabled ? BST_CHECKED : BST_UNCHECKED);
-      SubmitReportChecked(hwndDlg);
-
-      HWND hwndComment = GetDlgItem(hwndDlg, IDC_COMMENTTEXT);
-      WNDPROC OldWndProc = (WNDPROC)SetWindowLongPtr(
-          hwndComment, GWLP_WNDPROC, (LONG_PTR)EditSubclassProc);
-
-      // Subclass comment edit control to get placeholder text
-      SetWindowLongPtr(hwndComment, GWLP_USERDATA, (LONG_PTR)OldWndProc);
-      wstring commentGrayText = Str(ST_COMMENTGRAYTEXT);
-      wchar_t* hMem = (wchar_t*)GlobalAlloc(
-          GPTR, (commentGrayText.length() + 1) * sizeof(wchar_t));
-      wcscpy(hMem, commentGrayText.c_str());
-      SetProp(hwndComment, L"PROP_GRAYTEXT", hMem);
-
-      hwnd = GetDlgItem(hwndDlg, IDC_INCLUDEURLCHECK);
-      GetRelativeRect(hwnd, hwndDlg, &rect);
-      long diff =
-          ResizeControl(hwnd, rect, Str(ST_CHECKURL), false, gCheckboxPadding);
-      maxdiff = std::max(diff, maxdiff);
-      SetDlgItemText(hwndDlg, IDC_INCLUDEURLCHECK, Str(ST_CHECKURL).c_str());
-
-      // want this on by default
-      if (CheckBoolKey(gCrashReporterKey.c_str(), INCLUDE_URL_VALUE,
-                       &enabled) &&
-          !enabled) {
-        CheckDlgButton(hwndDlg, IDC_INCLUDEURLCHECK, BST_UNCHECKED);
-      } else {
-        CheckDlgButton(hwndDlg, IDC_INCLUDEURLCHECK, BST_CHECKED);
-      }
-
-      SetDlgItemText(hwndDlg, IDC_PROGRESSTEXT,
-                     Str(ST_REPORTPRESUBMIT).c_str());
-
-      RECT closeRect;
-      HWND hwndClose = GetDlgItem(hwndDlg, IDC_CLOSEBUTTON);
-      GetRelativeRect(hwndClose, hwndDlg, &closeRect);
-
-      RECT restartRect;
-      HWND hwndRestart = GetDlgItem(hwndDlg, IDC_RESTARTBUTTON);
-      GetRelativeRect(hwndRestart, hwndDlg, &restartRect);
-
-      // set the close button text and shift the buttons around
-      // since the size may need to change
-      int sizeDiff = ResizeControl(hwndClose, closeRect, Str(ST_QUIT), true, 0);
-      restartRect.left -= sizeDiff;
-      restartRect.right -= sizeDiff;
-      SetDlgItemText(hwndDlg, IDC_CLOSEBUTTON, Str(ST_QUIT).c_str());
-
-      if (gRestartArgs.size() > 0) {
-        // Resize restart button to fit text
-        ResizeControl(hwndRestart, restartRect, Str(ST_RESTART), true, 0);
-        SetDlgItemText(hwndDlg, IDC_RESTARTBUTTON, Str(ST_RESTART).c_str());
-      } else {
-        // No restart arguments, so just hide the restart button
-        SetDlgItemVisible(hwndDlg, IDC_RESTARTBUTTON, false);
-      }
-      // See if we need to widen the window
-      // Leave 6 pixels on either side + 6 pixels between the buttons
-      int neededSize = closeRect.right - closeRect.left + restartRect.right -
-                       restartRect.left + 6 * 3;
-      GetClientRect(hwndDlg, &r);
-      // We may already have resized one of the checkboxes above
-      maxdiff = std::max(maxdiff, neededSize - (r.right - r.left));
-
-      if (maxdiff > 0) {
-        // widen window
-        GetWindowRect(hwndDlg, &r);
-        r.right += maxdiff;
-        MoveWindow(hwndDlg, r.left, r.top, r.right - r.left, r.bottom - r.top,
-                   TRUE);
-        // shift both buttons right
-        if (restartRect.left + maxdiff < 6) maxdiff += 6;
-        closeRect.left += maxdiff;
-        closeRect.right += maxdiff;
-        restartRect.left += maxdiff;
-        restartRect.right += maxdiff;
-        MoveWindow(hwndClose, closeRect.left, closeRect.top,
-                   closeRect.right - closeRect.left,
-                   closeRect.bottom - closeRect.top, TRUE);
-        StretchControlsToFit(hwndDlg);
-      }
-      // need to move the restart button regardless
-      MoveWindow(hwndRestart, restartRect.left, restartRect.top,
-                 restartRect.right - restartRect.left,
-                 restartRect.bottom - restartRect.top, TRUE);
-
-      // Resize the description text last, in case the window was resized
-      // before this.
-      SendDlgItemMessage(hwndDlg, IDC_DESCRIPTIONTEXT, EM_SETEVENTMASK,
-                         (WPARAM) nullptr, ENM_REQUESTRESIZE);
-
-      wstring description = Str(ST_CRASHREPORTERHEADER);
-      description += L"\n\n";
-      description += Str(ST_CRASHREPORTERDESCRIPTION);
-      SetDlgItemText(hwndDlg, IDC_DESCRIPTIONTEXT, description.c_str());
-
-      // Make the title bold.
-      CHARFORMAT fmt = {
-          0,
-      };
-      fmt.cbSize = sizeof(fmt);
-      fmt.dwMask = CFM_BOLD;
-      fmt.dwEffects = CFE_BOLD;
-      SendDlgItemMessage(hwndDlg, IDC_DESCRIPTIONTEXT, EM_SETSEL, 0,
-                         Str(ST_CRASHREPORTERHEADER).length());
-      SendDlgItemMessage(hwndDlg, IDC_DESCRIPTIONTEXT, EM_SETCHARFORMAT,
-                         SCF_SELECTION, (LPARAM)&fmt);
-      SendDlgItemMessage(hwndDlg, IDC_DESCRIPTIONTEXT, EM_SETSEL, 0, 0);
-      // Force redraw.
-      SendDlgItemMessage(hwndDlg, IDC_DESCRIPTIONTEXT, EM_SETTARGETDEVICE,
-                         (WPARAM) nullptr, 0);
-      // Force resize.
-      SendDlgItemMessage(hwndDlg, IDC_DESCRIPTIONTEXT, EM_REQUESTRESIZE, 0, 0);
-
-      // if no URL was given, hide the URL checkbox
-      if (!gQueryParameters.isMember("URL")) {
-        RECT urlCheckRect;
-        GetWindowRect(GetDlgItem(hwndDlg, IDC_INCLUDEURLCHECK), &urlCheckRect);
-
-        SetDlgItemVisible(hwndDlg, IDC_INCLUDEURLCHECK, false);
-
-        gAttachedBottom.erase(IDC_VIEWREPORTBUTTON);
-        gAttachedBottom.erase(IDC_SUBMITREPORTCHECK);
-        gAttachedBottom.erase(IDC_COMMENTTEXT);
-
-        StretchDialog(hwndDlg, urlCheckRect.top - urlCheckRect.bottom);
-
-        gAttachedBottom.insert(IDC_VIEWREPORTBUTTON);
-        gAttachedBottom.insert(IDC_SUBMITREPORTCHECK);
-        gAttachedBottom.insert(IDC_COMMENTTEXT);
-      }
-
-      MaybeResizeProgressText(hwndDlg);
-
-      // Open the AVI resource for the throbber
-      Animate_Open(GetDlgItem(hwndDlg, IDC_THROBBER),
-                   MAKEINTRESOURCE(IDR_THROBBER));
-
-      UpdateURL(hwndDlg);
-
-      SetFocus(GetDlgItem(hwndDlg, IDC_SUBMITREPORTCHECK));
-      return FALSE;
-    }
-    case WM_SIZE: {
-      ReflowDialog(hwndDlg, HIWORD(lParam) - sHeight);
-      sHeight = HIWORD(lParam);
-      InvalidateRect(hwndDlg, nullptr, TRUE);
-      return FALSE;
-    }
-    case WM_NOTIFY: {
-      NMHDR* notification = reinterpret_cast<NMHDR*>(lParam);
-      if (notification->code == EN_REQUESTRESIZE) {
-        // Resizing the rich edit control to fit the description text.
-        REQRESIZE* reqresize = reinterpret_cast<REQRESIZE*>(lParam);
-        RECT newSize = reqresize->rc;
-        RECT oldSize;
-        GetRelativeRect(notification->hwndFrom, hwndDlg, &oldSize);
-
-        // resize the text box as requested
-        MoveWindow(notification->hwndFrom, newSize.left, newSize.top,
-                   newSize.right - newSize.left, newSize.bottom - newSize.top,
-                   TRUE);
-
-        // Resize the dialog to fit (the WM_SIZE handler will move the controls)
-        StretchDialog(hwndDlg, newSize.bottom - oldSize.bottom);
-      }
-      return FALSE;
-    }
-    case WM_COMMAND: {
-      if (HIWORD(wParam) == BN_CLICKED) {
-        switch (LOWORD(wParam)) {
-          case IDC_VIEWREPORTBUTTON:
-            DialogBoxParamMaybeRTL(IDD_VIEWREPORTDIALOG, hwndDlg,
-                                   (DLGPROC)ViewReportDialogProc, 0);
-            break;
-          case IDC_SUBMITREPORTCHECK:
-            SubmitReportChecked(hwndDlg);
-            break;
-          case IDC_INCLUDEURLCHECK:
-            UpdateURL(hwndDlg);
-            break;
-          case IDC_CLOSEBUTTON:
-            MaybeSendReport(hwndDlg);
-            break;
-          case IDC_RESTARTBUTTON:
-            RestartApplication();
-            MaybeSendReport(hwndDlg);
-            break;
-        }
-      } else if (HIWORD(wParam) == EN_CHANGE) {
-        switch (LOWORD(wParam)) {
-          case IDC_COMMENTTEXT:
-            UpdateComment(hwndDlg);
-        }
-      }
-
-      return FALSE;
-    }
-    case WM_UPLOADCOMPLETE: {
-      WaitForSingleObject(gThreadHandle, INFINITE);
-      success = (wParam == 1);
-      SendCompleted(success, WideToUTF8(gSendData.serverResponse));
-      // hide throbber
-      Animate_Stop(GetDlgItem(hwndDlg, IDC_THROBBER));
-      SetDlgItemVisible(hwndDlg, IDC_THROBBER, false);
-
-      SetDlgItemText(hwndDlg, IDC_PROGRESSTEXT,
-                     success ? Str(ST_REPORTSUBMITSUCCESS).c_str()
-                             : Str(ST_SUBMITFAILED).c_str());
-      MaybeResizeProgressText(hwndDlg);
-      // close dialog after 5 seconds
-      SetTimer(hwndDlg, 0, 5000, nullptr);
-      //
-      return TRUE;
-    }
-
-    case WM_TIMER: {
-      // The "1" gets used down in UIShowCrashUI to indicate that we at least
-      // tried to send the report.
-      EndCrashReporterDialog(hwndDlg, 1);
-      return FALSE;
-    }
-
-    case WM_CLOSE: {
-      EndCrashReporterDialog(hwndDlg, 0);
-      return FALSE;
-    }
-  }
-  return FALSE;
-}
-
-static wstring UTF8ToWide(const string& utf8, bool* success) {
-  wchar_t* buffer = nullptr;
-  int buffer_size =
-      MultiByteToWideChar(CP_UTF8, 0, utf8.c_str(), -1, nullptr, 0);
-  if (buffer_size == 0) {
-    if (success) *success = false;
-    return L"";
-  }
-
-  buffer = new wchar_t[buffer_size];
-  if (buffer == nullptr) {
-    if (success) *success = false;
-    return L"";
-  }
-
-  MultiByteToWideChar(CP_UTF8, 0, utf8.c_str(), -1, buffer, buffer_size);
-  wstring str = buffer;
-  delete[] buffer;
-
-  if (success) *success = true;
-
-  return str;
-}
-
-static string WideToMBCP(const wstring& wide, unsigned int cp,
-                         bool* success = nullptr) {
-  char* buffer = nullptr;
-  int buffer_size = WideCharToMultiByte(cp, 0, wide.c_str(), -1, nullptr, 0,
-                                        nullptr, nullptr);
-  if (buffer_size == 0) {
-    if (success) *success = false;
-    return "";
-  }
-
-  buffer = new char[buffer_size];
-  if (buffer == nullptr) {
-    if (success) *success = false;
-    return "";
-  }
-
-  WideCharToMultiByte(cp, 0, wide.c_str(), -1, buffer, buffer_size, nullptr,
-                      nullptr);
-  string mb = buffer;
-  delete[] buffer;
-
-  if (success) *success = true;
-
-  return mb;
-}
-
-string WideToUTF8(const wstring& wide, bool* success) {
-  return WideToMBCP(wide, CP_UTF8, success);
-}
-
-/* === Crashreporter UI Functions === */
-
-bool UIInit() {
-  for (size_t i = 0; i < sizeof(kDefaultAttachedBottom) / sizeof(UINT); i++) {
-    gAttachedBottom.insert(kDefaultAttachedBottom[i]);
-  }
-
-  DoInitCommonControls();
-
-  return true;
-}
-
-void UIShutdown() {}
-
-void UIShowDefaultUI() {
-  MessageBox(nullptr, Str(ST_CRASHREPORTERDEFAULT).c_str(), L"Crash Reporter",
-             MB_OK | MB_ICONSTOP);
-}
-
-bool UIShowCrashUI(const StringTable& files, const Json::Value& queryParameters,
-                   const string& sendURL, const vector<string>& restartArgs) {
-  gSendData.hDlg = nullptr;
-  gSendData.sendURL = UTF8ToWide(sendURL);
-
-  for (StringTable::const_iterator i = files.begin(); i != files.end(); i++) {
-    gSendData.files[UTF8ToWide(i->first)] = UTF8ToWide(i->second);
-  }
-
-  gQueryParameters = queryParameters;
-
-  if (gQueryParameters.isMember("Vendor")) {
-    gCrashReporterKey = L"Software\\";
-    string vendor = gQueryParameters["Vendor"].asString();
-    if (!vendor.empty()) {
-      gCrashReporterKey += UTF8ToWide(vendor) + L"\\";
-    }
-    string productName = gQueryParameters["ProductName"].asString();
-    gCrashReporterKey += UTF8ToWide(productName) + L"\\Crash Reporter";
-  }
-
-  if (gQueryParameters.isMember("URL")) {
-    gURLParameter = gQueryParameters["URL"].asString();
-  }
-
-  gRestartArgs = restartArgs;
-
-  if (gStrings.find("isRTL") != gStrings.end() && gStrings["isRTL"] == "yes")
-    gRTLlayout = true;
-
-  if (gAutoSubmit) {
-    gSendData.queryParameters = gQueryParameters;
-
-    gThreadHandle =
-        CreateThread(nullptr, 0, SendThreadProc, &gSendData, 0, nullptr);
-    WaitForSingleObject(gThreadHandle, INFINITE);
-    // SendCompleted was called from SendThreadProc
-    return true;
-  }
-
-  return 1 == DialogBoxParamMaybeRTL(IDD_SENDDIALOG, nullptr,
-                                     (DLGPROC)CrashReporterDialogProc, 0);
-}
-
-void UIError_impl(const string& message) {
-  wstring title = Str(ST_CRASHREPORTERTITLE);
-  if (title.empty()) title = L"Crash Reporter Error";
-
-  MessageBox(nullptr, UTF8ToWide(message).c_str(), title.c_str(),
-             MB_OK | MB_ICONSTOP);
-}
-
-bool UIGetIniPath(string& path) {
-  wchar_t fileName[MAX_PATH];
-  if (GetModuleFileName(nullptr, fileName, MAX_PATH)) {
-    // get crashreporter ini
-    wchar_t* s = wcsrchr(fileName, '.');
-    if (s) {
-      wcscpy(s, L".ini");
-      path = WideToUTF8(fileName);
-      return true;
-    }
-  }
-
-  return false;
-}
-
-bool UIGetSettingsPath(const string& vendor, const string& product,
-                       string& settings_path) {
-  wchar_t path[MAX_PATH] = {};
-  HRESULT hRes = SHGetFolderPath(nullptr, CSIDL_APPDATA, nullptr, 0, path);
-  if (FAILED(hRes)) {
-    // This provides a fallback for getting the path to APPDATA by querying the
-    // registry when the call to SHGetFolderPath is unable to provide this path
-    // (Bug 513958).
-    HKEY key;
-    DWORD type, dwRes;
-    DWORD size = sizeof(path) - 1;
-    dwRes = ::RegOpenKeyExW(HKEY_CURRENT_USER,
-                            L"Software\\Microsoft\\Windows\\CurrentVersion\\Exp"
-                            L"lorer\\Shell Folders",
-                            0, KEY_READ, &key);
-    if (dwRes != ERROR_SUCCESS) return false;
-
-    dwRes =
-        RegQueryValueExW(key, L"AppData", nullptr, &type, (LPBYTE)&path, &size);
-    ::RegCloseKey(key);
-    // The call to RegQueryValueExW must succeed, the type must be REG_SZ, the
-    // buffer size must not equal 0, and the buffer size be a multiple of 2.
-    if (dwRes != ERROR_SUCCESS || type != REG_SZ || size == 0 || size % 2 != 0)
-      return false;
-  }
-
-  if (!vendor.empty()) {
-    PathAppend(path, UTF8ToWide(vendor).c_str());
-  }
-  PathAppend(path, UTF8ToWide(product).c_str());
-  PathAppend(path, L"Crash Reports");
-  settings_path = WideToUTF8(path);
-  return true;
-}
-
-bool UIEnsurePathExists(const string& path) {
-  if (CreateDirectory(UTF8ToWide(path).c_str(), nullptr) == 0) {
-    if (GetLastError() != ERROR_ALREADY_EXISTS) return false;
-  }
-
-  return true;
-}
-
-bool UIFileExists(const string& path) {
-  DWORD attrs = GetFileAttributes(UTF8ToWide(path).c_str());
-  return (attrs != INVALID_FILE_ATTRIBUTES);
-}
-
-bool UIMoveFile(const string& oldfile, const string& newfile) {
-  if (oldfile == newfile) return true;
-
-  return MoveFile(UTF8ToWide(oldfile).c_str(), UTF8ToWide(newfile).c_str()) ==
-         TRUE;
-}
-
-bool UIDeleteFile(const string& oldfile) {
-  return DeleteFile(UTF8ToWide(oldfile).c_str()) == TRUE;
-}
-
-ifstream* UIOpenRead(const string& filename, ios_base::openmode mode) {
-#if defined(_MSC_VER)
-  ifstream* file = new ifstream();
-  file->open(UTF8ToWide(filename).c_str(), mode);
-#else   // GCC
-  ifstream* file =
-      new ifstream(WideToMBCP(UTF8ToWide(filename), CP_ACP).c_str(), mode);
-#endif  // _MSC_VER
-
-  return file;
-}
-
-ofstream* UIOpenWrite(const string& filename, ios_base::openmode mode) {
-#if defined(_MSC_VER)
-  ofstream* file = new ofstream();
-  file->open(UTF8ToWide(filename).c_str(), mode);
-#else   // GCC
-  ofstream* file =
-      new ofstream(WideToMBCP(UTF8ToWide(filename), CP_ACP).c_str(), mode);
-#endif  // _MSC_VER
-
-  return file;
-}
-
-struct FileData {
-  FILETIME timestamp;
-  wstring path;
-};
-
-static bool CompareFDTime(const FileData& fd1, const FileData& fd2) {
-  return CompareFileTime(&fd1.timestamp, &fd2.timestamp) > 0;
-}
-
-void UIPruneSavedDumps(const std::string& directory) {
-  wstring wdirectory = UTF8ToWide(directory);
-
-  WIN32_FIND_DATA fdata;
-  wstring findpath = wdirectory + L"\\*.dmp";
-  HANDLE dirlist = FindFirstFile(findpath.c_str(), &fdata);
-  if (dirlist == INVALID_HANDLE_VALUE) return;
-
-  vector<FileData> dumpfiles;
-
-  for (BOOL ok = true; ok; ok = FindNextFile(dirlist, &fdata)) {
-    FileData fd = {fdata.ftLastWriteTime, wdirectory + L"\\" + fdata.cFileName};
-    dumpfiles.push_back(fd);
-  }
-
-  sort(dumpfiles.begin(), dumpfiles.end(), CompareFDTime);
-
-  while (dumpfiles.size() > kSaveCount) {
-    // get the path of the oldest file
-    wstring path = (--dumpfiles.end())->path;
-    DeleteFile(path.c_str());
-
-    // s/.dmp/.extra/
-    path.replace(path.size() - 4, 4, L".extra");
-    DeleteFile(path.c_str());
-
-    dumpfiles.pop_back();
-  }
-  FindClose(dirlist);
-}
-
-bool UIRunProgram(const string& exename, const std::vector<std::string>& args,
-                  bool wait) {
-  wstring cmdLine = L"\"" + UTF8ToWide(exename) + L"\" ";
-
-  for (auto arg : args) {
-    cmdLine += L"\"" + UTF8ToWide(arg) + L"\" ";
-  }
-
-  STARTUPINFO si = {};
-  si.cb = sizeof(si);
-  PROCESS_INFORMATION pi = {};
-
-  if (!CreateProcess(/* lpApplicationName */ nullptr, (LPWSTR)cmdLine.c_str(),
-                     /* lpProcessAttributes */ nullptr,
-                     /* lpThreadAttributes */ nullptr,
-                     /* bInheritHandles */ false,
-                     NORMAL_PRIORITY_CLASS | CREATE_NO_WINDOW,
-                     /* lpEnvironment */ nullptr,
-                     /* lpCurrentDirectory */ nullptr, &si, &pi)) {
-    return false;
-  }
-
-  if (wait) {
-    WaitForSingleObject(pi.hProcess, INFINITE);
-  }
-
-  CloseHandle(pi.hProcess);
-  CloseHandle(pi.hThread);
-  return true;
-}
-
-string UIGetEnv(const string& name) {
-  const wchar_t* var = _wgetenv(UTF8ToWide(name).c_str());
-  if (var && *var) {
-    return WideToUTF8(var);
-  }
-
-  return "";
-}
diff --git a/toolkit/crashreporter/client/gtkbind/Cargo.toml b/toolkit/crashreporter/client/gtkbind/Cargo.toml
new file mode 100644
index 0000000000..813d43dbe3
--- /dev/null
+++ b/toolkit/crashreporter/client/gtkbind/Cargo.toml
@@ -0,0 +1,8 @@
+[package]
+name = "gtkbind"
+version = "0.1.0"
+edition = "2021"
+
+[build-dependencies]
+bindgen = { version = "0.69.0", default-features = false, features = ["runtime"] }
+mozbuild = "0.1.0"
diff --git a/toolkit/crashreporter/client/gtkbind/build.rs b/toolkit/crashreporter/client/gtkbind/build.rs
new file mode 100644
index 0000000000..fa3402fdf2
--- /dev/null
+++ b/toolkit/crashreporter/client/gtkbind/build.rs
@@ -0,0 +1,43 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+use mozbuild::config::{
+    CC_BASE_FLAGS as CFLAGS, MOZ_GTK3_CFLAGS as GTK_CFLAGS, MOZ_GTK3_LIBS as GTK_LIBS,
+};
+
+const HEADER: &str = r#"
+#include "gtk/gtk.h"
+#include "pango/pango.h"
+#include "gdk-pixbuf/gdk-pixbuf.h"
+"#;
+
+fn main() {
+    let bindings = bindgen::Builder::default()
+        .header_contents("gtk_bindings.h", HEADER)
+        .clang_args(CFLAGS)
+        .clang_args(GTK_CFLAGS)
+        .allowlist_function("gtk_.*")
+        .allowlist_function(
+            "g_(application|main_context|memory_input_stream|object|signal|timeout)_.*",
+        )
+        .allowlist_function("gdk_pixbuf_new_from_stream")
+        .allowlist_function("pango_attr_.*")
+        // The gtk/glib valist functions generate FFI-unsafe signatures on aarch64 which cause
+        // compile errors. We don't use them anyway.
+        .blocklist_function(".*_valist")
+        .derive_default(true)
+        .generate()
+        .expect("unable to generate gtk bindings");
+    for flag in GTK_LIBS {
+        if let Some(lib) = flag.strip_prefix("-l") {
+            println!("cargo:rustc-link-lib={lib}");
+        } else if let Some(path) = flag.strip_prefix("-L") {
+            println!("cargo:rustc-link-search={path}");
+        }
+    }
+    let out_path = std::path::PathBuf::from(std::env::var("OUT_DIR").unwrap());
+    bindings
+        .write_to_file(out_path.join("gtk_bindings.rs"))
+        .expect("failed to write gtk bindings");
+}
diff --git a/toolkit/crashreporter/process_reader/src/process_reader.rs b/toolkit/crashreporter/client/gtkbind/src/lib.rs
index 1473aafa09..714f3ed047 100644
--- a/toolkit/crashreporter/process_reader/src/process_reader.rs
+++ b/toolkit/crashreporter/client/gtkbind/src/lib.rs
@@ -2,5 +2,8 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
-#[cfg(target_os = "windows")]
-mod windows;
+#![allow(non_upper_case_globals)]
+#![allow(non_camel_case_types)]
+#![allow(non_snake_case)]
+
+include!(concat!(env!("OUT_DIR"), "/gtk_bindings.rs"));
diff --git a/toolkit/crashreporter/client/macbuild/Contents/Resources/English.lproj/MainMenu.nib/classes.nib b/toolkit/crashreporter/client/macbuild/Contents/Resources/English.lproj/MainMenu.nib/classes.nib
deleted file mode 100644
index 254131e431..0000000000
--- a/toolkit/crashreporter/client/macbuild/Contents/Resources/English.lproj/MainMenu.nib/classes.nib
+++ /dev/null
@@ -1,100 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
-<plist version="1.0">
-<dict>
-	<key>IBClasses</key>
-	<array>
-		<dict>
-			<key>ACTIONS</key>
-			<dict>
-				<key>closeClicked</key>
-				<string>id</string>
-				<key>includeURLClicked</key>
-				<string>id</string>
-				<key>restartClicked</key>
-				<string>id</string>
-				<key>submitReportClicked</key>
-				<string>id</string>
-				<key>viewReportClicked</key>
-				<string>id</string>
-				<key>viewReportOkClicked</key>
-				<string>id</string>
-			</dict>
-			<key>CLASS</key>
-			<string>CrashReporterUI</string>
-			<key>LANGUAGE</key>
-			<string>ObjC</string>
-			<key>OUTLETS</key>
-			<dict>
-				<key>mCloseButton</key>
-				<string>NSButton</string>
-				<key>mCommentScrollView</key>
-				<string>NSScrollView</string>
-				<key>mCommentText</key>
-				<string>TextViewWithPlaceHolder</string>
-				<key>mDescriptionLabel</key>
-				<string>NSTextField</string>
-				<key>mEmailMeButton</key>
-				<string>NSButton</string>
-				<key>mEmailText</key>
-				<string>NSTextField</string>
-				<key>mErrorCloseButton</key>
-				<string>NSButton</string>
-				<key>mErrorHeaderLabel</key>
-				<string>NSTextField</string>
-				<key>mErrorLabel</key>
-				<string>NSTextField</string>
-				<key>mErrorView</key>
-				<string>NSView</string>
-				<key>mHeaderLabel</key>
-				<string>NSTextField</string>
-				<key>mIncludeURLButton</key>
-				<string>NSButton</string>
-				<key>mProgressIndicator</key>
-				<string>NSProgressIndicator</string>
-				<key>mProgressText</key>
-				<string>NSTextField</string>
-				<key>mRestartButton</key>
-				<string>NSButton</string>
-				<key>mSubmitReportButton</key>
-				<string>NSButton</string>
-				<key>mViewReportButton</key>
-				<string>NSButton</string>
-				<key>mViewReportOkButton</key>
-				<string>NSButton</string>
-				<key>mViewReportTextView</key>
-				<string>NSTextView</string>
-				<key>mViewReportWindow</key>
-				<string>NSWindow</string>
-				<key>mWindow</key>
-				<string>NSWindow</string>
-			</dict>
-			<key>SUPERCLASS</key>
-			<string>NSObject</string>
-		</dict>
-		<dict>
-			<key>ACTIONS</key>
-			<dict>
-				<key>insertTab</key>
-				<string>id</string>
-			</dict>
-			<key>CLASS</key>
-			<string>TextViewWithPlaceHolder</string>
-			<key>LANGUAGE</key>
-			<string>ObjC</string>
-			<key>SUPERCLASS</key>
-			<string>NSTextView</string>
-		</dict>
-		<dict>
-			<key>CLASS</key>
-			<string>FirstResponder</string>
-			<key>LANGUAGE</key>
-			<string>ObjC</string>
-			<key>SUPERCLASS</key>
-			<string>NSObject</string>
-		</dict>
-	</array>
-	<key>IBVersion</key>
-	<string>1</string>
-</dict>
-</plist>
diff --git a/toolkit/crashreporter/client/macbuild/Contents/Resources/English.lproj/MainMenu.nib/info.nib b/toolkit/crashreporter/client/macbuild/Contents/Resources/English.lproj/MainMenu.nib/info.nib
deleted file mode 100644
index 517349ffce..0000000000
--- a/toolkit/crashreporter/client/macbuild/Contents/Resources/English.lproj/MainMenu.nib/info.nib
+++ /dev/null
@@ -1,18 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
-<plist version="1.0">
-<dict>
-	<key>IBFramework Version</key>
-	<string>629</string>
-	<key>IBOldestOS</key>
-	<integer>5</integer>
-	<key>IBOpenObjects</key>
-	<array>
-		<integer>2</integer>
-	</array>
-	<key>IBSystem Version</key>
-	<string>9C7010</string>
-	<key>targetFramework</key>
-	<string>IBCocoaFramework</string>
-</dict>
-</plist>
diff --git a/toolkit/crashreporter/client/macbuild/Contents/Resources/English.lproj/MainMenu.nib/keyedobjects.nib b/toolkit/crashreporter/client/macbuild/Contents/Resources/English.lproj/MainMenu.nib/keyedobjects.nib
deleted file mode 100644
index bfdcccb74c..0000000000
--- a/toolkit/crashreporter/client/macbuild/Contents/Resources/English.lproj/MainMenu.nib/keyedobjects.nib
+++ /dev/null
diff --git a/toolkit/crashreporter/client/macbuild/Contents/Resources/English.lproj/MainMenuRTL.nib/classes.nib b/toolkit/crashreporter/client/macbuild/Contents/Resources/English.lproj/MainMenuRTL.nib/classes.nib
deleted file mode 100644
index 254131e431..0000000000
--- a/toolkit/crashreporter/client/macbuild/Contents/Resources/English.lproj/MainMenuRTL.nib/classes.nib
+++ /dev/null
@@ -1,100 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
-<plist version="1.0">
-<dict>
-	<key>IBClasses</key>
-	<array>
-		<dict>
-			<key>ACTIONS</key>
-			<dict>
-				<key>closeClicked</key>
-				<string>id</string>
-				<key>includeURLClicked</key>
-				<string>id</string>
-				<key>restartClicked</key>
-				<string>id</string>
-				<key>submitReportClicked</key>
-				<string>id</string>
-				<key>viewReportClicked</key>
-				<string>id</string>
-				<key>viewReportOkClicked</key>
-				<string>id</string>
-			</dict>
-			<key>CLASS</key>
-			<string>CrashReporterUI</string>
-			<key>LANGUAGE</key>
-			<string>ObjC</string>
-			<key>OUTLETS</key>
-			<dict>
-				<key>mCloseButton</key>
-				<string>NSButton</string>
-				<key>mCommentScrollView</key>
-				<string>NSScrollView</string>
-				<key>mCommentText</key>
-				<string>TextViewWithPlaceHolder</string>
-				<key>mDescriptionLabel</key>
-				<string>NSTextField</string>
-				<key>mEmailMeButton</key>
-				<string>NSButton</string>
-				<key>mEmailText</key>
-				<string>NSTextField</string>
-				<key>mErrorCloseButton</key>
-				<string>NSButton</string>
-				<key>mErrorHeaderLabel</key>
-				<string>NSTextField</string>
-				<key>mErrorLabel</key>
-				<string>NSTextField</string>
-				<key>mErrorView</key>
-				<string>NSView</string>
-				<key>mHeaderLabel</key>
-				<string>NSTextField</string>
-				<key>mIncludeURLButton</key>
-				<string>NSButton</string>
-				<key>mProgressIndicator</key>
-				<string>NSProgressIndicator</string>
-				<key>mProgressText</key>
-				<string>NSTextField</string>
-				<key>mRestartButton</key>
-				<string>NSButton</string>
-				<key>mSubmitReportButton</key>
-				<string>NSButton</string>
-				<key>mViewReportButton</key>
-				<string>NSButton</string>
-				<key>mViewReportOkButton</key>
-				<string>NSButton</string>
-				<key>mViewReportTextView</key>
-				<string>NSTextView</string>
-				<key>mViewReportWindow</key>
-				<string>NSWindow</string>
-				<key>mWindow</key>
-				<string>NSWindow</string>
-			</dict>
-			<key>SUPERCLASS</key>
-			<string>NSObject</string>
-		</dict>
-		<dict>
-			<key>ACTIONS</key>
-			<dict>
-				<key>insertTab</key>
-				<string>id</string>
-			</dict>
-			<key>CLASS</key>
-			<string>TextViewWithPlaceHolder</string>
-			<key>LANGUAGE</key>
-			<string>ObjC</string>
-			<key>SUPERCLASS</key>
-			<string>NSTextView</string>
-		</dict>
-		<dict>
-			<key>CLASS</key>
-			<string>FirstResponder</string>
-			<key>LANGUAGE</key>
-			<string>ObjC</string>
-			<key>SUPERCLASS</key>
-			<string>NSObject</string>
-		</dict>
-	</array>
-	<key>IBVersion</key>
-	<string>1</string>
-</dict>
-</plist>
diff --git a/toolkit/crashreporter/client/macbuild/Contents/Resources/English.lproj/MainMenuRTL.nib/info.nib b/toolkit/crashreporter/client/macbuild/Contents/Resources/English.lproj/MainMenuRTL.nib/info.nib
deleted file mode 100644
index 4a2251aaf5..0000000000
--- a/toolkit/crashreporter/client/macbuild/Contents/Resources/English.lproj/MainMenuRTL.nib/info.nib
+++ /dev/null
@@ -1,18 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
-<plist version="1.0">
-<dict>
-	<key>IBFramework Version</key>
-	<string>629</string>
-	<key>IBOldestOS</key>
-	<integer>5</integer>
-	<key>IBOpenObjects</key>
-	<array>
-		<integer>2</integer>
-	</array>
-	<key>IBSystem Version</key>
-	<string>9D34</string>
-	<key>targetFramework</key>
-	<string>IBCocoaFramework</string>
-</dict>
-</plist>
diff --git a/toolkit/crashreporter/client/macbuild/Contents/Resources/English.lproj/MainMenuRTL.nib/keyedobjects.nib b/toolkit/crashreporter/client/macbuild/Contents/Resources/English.lproj/MainMenuRTL.nib/keyedobjects.nib
deleted file mode 100644
index 6c93849b94..0000000000
--- a/toolkit/crashreporter/client/macbuild/Contents/Resources/English.lproj/MainMenuRTL.nib/keyedobjects.nib
+++ /dev/null
diff --git a/toolkit/crashreporter/client/moz.build b/toolkit/crashreporter/client/moz.build
deleted file mode 100644
index 82e19b8637..0000000000
--- a/toolkit/crashreporter/client/moz.build
+++ /dev/null
@@ -1,97 +0,0 @@
-# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
-# vim: set filetype=python:
-# This Source Code Form is subject to the terms of the Mozilla Public
-# License, v. 2.0. If a copy of the MPL was not distributed with this
-# file, You can obtain one at http://mozilla.org/MPL/2.0/.
-
-if CONFIG["OS_TARGET"] != "Android":
-    Program("crashreporter")
-
-    UNIFIED_SOURCES += [
-        "../CrashAnnotations.cpp",
-        "crashreporter.cpp",
-        "ping.cpp",
-    ]
-
-    LOCAL_INCLUDES += [
-        "/toolkit/components/jsoncpp/include",
-    ]
-
-    USE_LIBS += [
-        "jsoncpp",
-    ]
-
-if CONFIG["OS_ARCH"] == "WINNT":
-    UNIFIED_SOURCES += [
-        "crashreporter_win.cpp",
-    ]
-    include("/toolkit/crashreporter/breakpad-client/windows/sender/objs.mozbuild")
-    SOURCES += objs_sender
-    SOURCES += [
-        "../google-breakpad/src/common/windows/http_upload.cc",
-    ]
-    DEFINES["UNICODE"] = True
-    DEFINES["_UNICODE"] = True
-    USE_LIBS += [
-        "nss",
-    ]
-    OS_LIBS += [
-        "advapi32",
-        "comctl32",
-        "gdi32",
-        "ole32",
-        "shell32",
-        "wininet",
-        "shlwapi",
-        "user32",
-    ]
-elif CONFIG["OS_ARCH"] == "Darwin":
-    UNIFIED_SOURCES += [
-        "../google-breakpad/src/common/mac/HTTPMultipartUpload.m",
-        "crashreporter_osx.mm",
-        "crashreporter_unix_common.cpp",
-    ]
-    LOCAL_INCLUDES += [
-        "../google-breakpad/src/common/mac",
-    ]
-    OS_LIBS += ["-framework Cocoa"]
-    USE_LIBS += [
-        "nss",
-    ]
-    LDFLAGS += ["-Wl,-rpath,@executable_path/../../../"]
-elif CONFIG["OS_ARCH"] == "SunOS":
-    SOURCES += [
-        "crashreporter_linux.cpp",
-        "crashreporter_unix.cpp",
-    ]
-    USE_LIBS += [
-        "breakpad_solaris_common_s",
-    ]
-
-if CONFIG["MOZ_WIDGET_TOOLKIT"] == "gtk":
-    UNIFIED_SOURCES += [
-        "../google-breakpad/src/common/linux/http_upload.cc",
-        "crashreporter_gtk_common.cpp",
-        "crashreporter_linux.cpp",
-        "crashreporter_unix_common.cpp",
-    ]
-    OS_LIBS += CONFIG["MOZ_GTK3_LIBS"]
-    OS_LIBS += CONFIG["MOZ_GTHREAD_LIBS"]
-    CXXFLAGS += CONFIG["MOZ_GTK3_CFLAGS"]
-    CXXFLAGS += CONFIG["MOZ_GTHREAD_CFLAGS"]
-
-if CONFIG["OS_ARCH"] == "Linux" or CONFIG["OS_ARCH"] == "SunOS":
-    FINAL_TARGET_FILES += [
-        "Throbber-small.gif",
-    ]
-
-DEFINES["MOZ_APP_NAME"] = '"%s"' % CONFIG["MOZ_APP_NAME"]
-DEFINES["BIN_SUFFIX"] = '"%s"' % CONFIG["BIN_SUFFIX"]
-
-RCINCLUDE = "crashreporter.rc"
-
-# Don't use the STL wrappers in the crashreporter clients; they don't
-# link with -lmozalloc, and it really doesn't matter here anyway.
-DisableStlWrapping()
-
-include("/toolkit/crashreporter/crashreporter.mozbuild")
diff --git a/toolkit/crashreporter/client/ping.cpp b/toolkit/crashreporter/client/ping.cpp
deleted file mode 100644
index b49211c9c1..0000000000
--- a/toolkit/crashreporter/client/ping.cpp
+++ /dev/null
@@ -1,324 +0,0 @@
-/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-#include "crashreporter.h"
-
-#include <cstring>
-#include <ctime>
-#include <string>
-
-#if defined(XP_LINUX)
-#  include <fcntl.h>
-#  include <unistd.h>
-#  include <sys/stat.h>
-#elif defined(XP_MACOSX)
-#  include <CoreFoundation/CoreFoundation.h>
-#elif defined(XP_WIN)
-#  include <objbase.h>
-#endif
-
-#include "json/json.h"
-
-#include "CrashAnnotations.h"
-
-using std::string;
-
-namespace CrashReporter {
-
-struct UUID {
-  uint32_t m0;
-  uint16_t m1;
-  uint16_t m2;
-  uint8_t m3[8];
-};
-
-// Generates an UUID; the code here is mostly copied from nsUUIDGenerator.cpp
-static string GenerateUUID() {
-  UUID id = {};
-
-#if defined(XP_WIN)  // Windows
-  HRESULT hr = CoCreateGuid((GUID*)&id);
-  if (FAILED(hr)) {
-    return "";
-  }
-#elif defined(XP_MACOSX)            // MacOS X
-  CFUUIDRef uuid = CFUUIDCreate(kCFAllocatorDefault);
-  if (!uuid) {
-    return "";
-  }
-
-  CFUUIDBytes bytes = CFUUIDGetUUIDBytes(uuid);
-  memcpy(&id, &bytes, sizeof(UUID));
-
-  CFRelease(uuid);
-#elif defined(HAVE_ARC4RANDOM_BUF)  // Android, BSD, ...
-  arc4random_buf(&id, sizeof(UUID));
-#else                               // Linux
-  int fd = open("/dev/urandom", O_RDONLY);
-
-  if (fd == -1) {
-    return "";
-  }
-
-  if (read(fd, &id, sizeof(UUID)) != sizeof(UUID)) {
-    close(fd);
-    return "";
-  }
-
-  close(fd);
-#endif
-
-  /* Put in the version */
-  id.m2 &= 0x0fff;
-  id.m2 |= 0x4000;
-
-  /* Put in the variant */
-  id.m3[0] &= 0x3f;
-  id.m3[0] |= 0x80;
-
-  const char* kUUIDFormatString =
-      "%08x-%04x-%04x-%02x%02x-%02x%02x%02x%02x%02x%02x";
-  const size_t kUUIDFormatStringLength = 36;
-  char str[kUUIDFormatStringLength + 1] = {'\0'};
-
-  int num = snprintf(str, kUUIDFormatStringLength + 1, kUUIDFormatString, id.m0,
-                     id.m1, id.m2, id.m3[0], id.m3[1], id.m3[2], id.m3[3],
-                     id.m3[4], id.m3[5], id.m3[6], id.m3[7]);
-
-  if (num != kUUIDFormatStringLength) {
-    return "";
-  }
-
-  return str;
-}
-
-const char kISO8601Date[] = "%F";
-const char kISO8601DateHours[] = "%FT%H:00:00.000Z";
-
-// Return the current date as a string in the specified format, the following
-// constants are provided:
-// - kISO8601Date, the ISO 8601 date format, YYYY-MM-DD
-// - kISO8601DateHours, the ISO 8601 full date format, YYYY-MM-DDTHH:00:00.000Z
-static string CurrentDate(string format) {
-  time_t now;
-  time(&now);
-  char buf[64];  // This should be plenty
-  strftime(buf, sizeof buf, format.c_str(), gmtime(&now));
-  return buf;
-}
-
-const char kTelemetryClientId[] = "TelemetryClientId";
-const char kTelemetryUrl[] = "TelemetryServerURL";
-const char kTelemetrySessionId[] = "TelemetrySessionId";
-const int kTelemetryVersion = 4;
-
-// Create the payload.metadata node of the crash ping using fields extracted
-// from the .extra file
-static Json::Value CreateMetadataNode(const Json::Value& aExtra) {
-  Json::Value node;
-
-  for (Json::ValueConstIterator iter = aExtra.begin(); iter != aExtra.end();
-       ++iter) {
-    Annotation annotation;
-
-    if (AnnotationFromString(annotation, iter.memberName())) {
-      if (IsAnnotationAllowedForPing(annotation)) {
-        node[iter.memberName()] = *iter;
-      }
-    }
-  }
-
-  return node;
-}
-
-// Create the payload node of the crash ping
-static Json::Value CreatePayloadNode(const Json::Value& aExtra,
-                                     const string& aHash,
-                                     const string& aSessionId) {
-  Json::Value payload;
-
-  payload["sessionId"] = aSessionId;
-  payload["version"] = 1;
-  payload["crashDate"] = CurrentDate(kISO8601Date);
-  payload["crashTime"] = CurrentDate(kISO8601DateHours);
-  payload["hasCrashEnvironment"] = true;
-  payload["crashId"] = CrashReporter::GetDumpLocalID();
-  payload["minidumpSha256Hash"] = aHash;
-  payload["processType"] = "main";  // This is always a main crash
-  if (aExtra.isMember("StackTraces")) {
-    payload["stackTraces"] = aExtra["StackTraces"];
-  }
-
-  // Assemble the payload metadata
-  payload["metadata"] = CreateMetadataNode(aExtra);
-
-  return payload;
-}
-
-// Create the application node of the crash ping
-static Json::Value CreateApplicationNode(
-    const string& aVendor, const string& aName, const string& aVersion,
-    const string& aDisplayVersion, const string& aPlatformVersion,
-    const string& aChannel, const string& aBuildId, const string& aArchitecture,
-    const string& aXpcomAbi) {
-  Json::Value application;
-
-  application["vendor"] = aVendor;
-  application["name"] = aName;
-  application["buildId"] = aBuildId;
-  application["displayVersion"] = aDisplayVersion;
-  application["platformVersion"] = aPlatformVersion;
-  application["version"] = aVersion;
-  application["channel"] = aChannel;
-  if (!aArchitecture.empty()) {
-    application["architecture"] = aArchitecture;
-  }
-  if (!aXpcomAbi.empty()) {
-    application["xpcomAbi"] = aXpcomAbi;
-  }
-
-  return application;
-}
-
-// Create the root node of the crash ping
-static Json::Value CreateRootNode(
-    const Json::Value& aExtra, const string& aUuid, const string& aHash,
-    const string& aClientId, const string& aSessionId, const string& aName,
-    const string& aVersion, const string& aChannel, const string& aBuildId) {
-  Json::Value root;
-  root["type"] = "crash";  // This is a crash ping
-  root["id"] = aUuid;
-  root["version"] = kTelemetryVersion;
-  root["creationDate"] = CurrentDate(kISO8601DateHours);
-  root["clientId"] = aClientId;
-
-  // Parse the telemetry environment
-  Json::Value environment;
-  Json::Reader reader;
-  string architecture;
-  string xpcomAbi;
-  string displayVersion;
-  string platformVersion;
-
-  if (reader.parse(aExtra["TelemetryEnvironment"].asString(), environment,
-                   /* collectComments */ false)) {
-    if (environment.isMember("build") && environment["build"].isObject()) {
-      Json::Value build = environment["build"];
-      if (build.isMember("architecture") && build["architecture"].isString()) {
-        architecture = build["architecture"].asString();
-      }
-      if (build.isMember("xpcomAbi") && build["xpcomAbi"].isString()) {
-        xpcomAbi = build["xpcomAbi"].asString();
-      }
-      if (build.isMember("displayVersion") &&
-          build["displayVersion"].isString()) {
-        displayVersion = build["displayVersion"].asString();
-      }
-      if (build.isMember("platformVersion") &&
-          build["platformVersion"].isString()) {
-        platformVersion = build["platformVersion"].asString();
-      }
-    }
-
-    root["environment"] = environment;
-  }
-
-  root["payload"] = CreatePayloadNode(aExtra, aHash, aSessionId);
-  root["application"] = CreateApplicationNode(
-      aExtra["Vendor"].asString(), aName, aVersion, displayVersion,
-      platformVersion, aChannel, aBuildId, architecture, xpcomAbi);
-
-  return root;
-}
-
-// Generates the URL used to submit the crash ping, see TelemetrySend.sys.mjs
-string GenerateSubmissionUrl(const string& aUrl, const string& aId,
-                             const string& aName, const string& aVersion,
-                             const string& aChannel, const string& aBuildId) {
-  return aUrl + "/submit/telemetry/" + aId + "/crash/" + aName + "/" +
-         aVersion + "/" + aChannel + "/" + aBuildId +
-         "?v=" + std::to_string(kTelemetryVersion);
-}
-
-// Write out the ping into the specified file.
-//
-// Returns true if the ping was written out successfully, false otherwise.
-static bool WritePing(const string& aPath, const string& aPing) {
-  std::ofstream* f = UIOpenWrite(aPath, std::ios::trunc);
-  bool success = false;
-
-  if (f->is_open()) {
-    *f << aPing;
-    f->close();
-    success = f->good();
-  }
-
-  delete f;
-  return success;
-}
-
-// Assembles the crash ping using the JSON data extracted from the .extra file
-// and sends it using the crash sender. All the telemetry specific data but the
-// environment will be stripped from the annotations so that it won't be sent
-// together with the crash report.
-//
-// Note that the crash ping sender is invoked in a fire-and-forget way so this
-// won't block waiting for the ping to be delivered.
-//
-// Returns true if the ping was assembled and handed over to the pingsender
-// correctly, also populates the aPingUuid parameter with the ping UUID. Returns
-// false otherwise and leaves the aPingUuid parameter unmodified.
-bool SendCrashPing(Json::Value& aExtra, const string& aHash, string& aPingUuid,
-                   const string& pingDir) {
-  // Remove the telemetry-related data from the crash annotations
-  Json::Value value;
-  aExtra.removeMember(kTelemetryClientId, &value);
-  string clientId = value.asString();
-  aExtra.removeMember(kTelemetryUrl, &value);
-  string serverUrl = value.asString();
-  aExtra.removeMember(kTelemetrySessionId, &value);
-  string sessionId = value.asString();
-
-  if (clientId.empty() || serverUrl.empty() || sessionId.empty()) {
-    return false;
-  }
-
-  string buildId = aExtra["BuildID"].asString();
-  string channel = aExtra["ReleaseChannel"].asString();
-  string name = aExtra["ProductName"].asString();
-  string version = aExtra["Version"].asString();
-  string uuid = GenerateUUID();
-  string url =
-      GenerateSubmissionUrl(serverUrl, uuid, name, version, channel, buildId);
-
-  if (serverUrl.empty() || uuid.empty()) {
-    return false;
-  }
-
-  Json::Value root = CreateRootNode(aExtra, uuid, aHash, clientId, sessionId,
-                                    name, version, channel, buildId);
-
-  // Write out the result to the pending pings directory
-  Json::StreamWriterBuilder builder;
-  builder["indentation"] = "";
-  string ping = Json::writeString(builder, root);
-  string pingPath = pingDir + UI_DIR_SEPARATOR + uuid + ".json";
-
-  if (!WritePing(pingPath, ping)) {
-    return false;
-  }
-
-  // Hand over the ping to the sender
-  std::vector<string> args = {url, pingPath};
-  if (UIRunProgram(CrashReporter::GetProgramPath(UI_PING_SENDER_FILENAME),
-                   args)) {
-    aPingUuid = uuid;
-    return true;
-  } else {
-    return false;
-  }
-}
-
-}  // namespace CrashReporter
diff --git a/toolkit/crashreporter/client/resource.h b/toolkit/crashreporter/client/resource.h
deleted file mode 100644
index 2e7917daa4..0000000000
--- a/toolkit/crashreporter/client/resource.h
+++ /dev/null
@@ -1,35 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-//{{NO_DEPENDENCIES}}
-// Microsoft Visual C++ generated include file.
-// Used by crashreporter.rc
-//
-#define IDD_SENDDIALOG 102
-#define IDR_THROBBER 103
-#define IDD_VIEWREPORTDIALOG 104
-#define IDI_MAINICON 105
-#define IDC_PROGRESS 1003
-#define IDC_DESCRIPTIONTEXT 1004
-#define IDC_CLOSEBUTTON 1005
-#define IDC_VIEWREPORTBUTTON 1006
-#define IDC_SUBMITREPORTCHECK 1007
-#define IDC_INCLUDEURLCHECK 1010
-#define IDC_COMMENTTEXT 1011
-#define IDC_RESTARTBUTTON 1012
-#define IDC_DESCRIPTIONLABEL 1013
-#define IDC_PROGRESSTEXT 1014
-#define IDC_THROBBER 1015
-#define IDC_VIEWREPORTTEXT 1016
-
-// Next default values for new objects
-//
-#ifdef APSTUDIO_INVOKED
-#  ifndef APSTUDIO_READONLY_SYMBOLS
-#    define _APS_NEXT_RESOURCE_VALUE 106
-#    define _APS_NEXT_COMMAND_VALUE 40001
-#    define _APS_NEXT_CONTROL_VALUE 1017
-#    define _APS_NEXT_SYMED_VALUE 101
-#  endif
-#endif
diff --git a/toolkit/crashreporter/docs/index.rst b/toolkit/crashreporter/docs/index.rst
index fe1af45d8f..d08c28fb92 100644
--- a/toolkit/crashreporter/docs/index.rst
+++ b/toolkit/crashreporter/docs/index.rst
@@ -258,6 +258,15 @@ Environment variables used internally
 - ``MOZ_CRASHREPORTER_STRINGS_OVERRIDE`` - Overrides the path used to load the
   .ini file holding the strings used in the crash reporter client UI.
 
+Environment variables used for development
+------------------------------------------
+
+Set these at build time (e.g. ``ac_add_options`` in ``.mozconfig``).
+
+- ``MOZ_CRASHREPORTER_MOCK`` - When set, causes the crash reporter client to
+  mock its interfaces to the system so that you can test the GUI behavior. The
+  GUI will not interact with the host system at all when this is set.
+
 Other topics
 ============
 
diff --git a/toolkit/crashreporter/moz.build b/toolkit/crashreporter/moz.build
index 952ca405bb..2fb1071de9 100644
--- a/toolkit/crashreporter/moz.build
+++ b/toolkit/crashreporter/moz.build
@@ -67,10 +67,12 @@ if CONFIG["MOZ_CRASHREPORTER"]:
             DIRS += ["rust_minidump_writer_linux"]
 
     if CONFIG["OS_TARGET"] != "Android":
-        DIRS += ["minidump-analyzer"]
+        DIRS += [
+            "client/app",
+            "minidump-analyzer",
+        ]
 
     DIRS += [
-        "client",
         "mozannotation_client",
         "mozannotation_server",
     ]
@@ -118,9 +120,12 @@ if CONFIG["MOZ_CRASHREPORTER"]:
         DEFINES["MOZ_PHC"] = True
 
     LOCAL_INCLUDES += [
+        "/toolkit/components/jsoncpp/include",
         "google-breakpad/src",
     ]
 
+    USE_LIBS += ["jsoncpp"]
+
     PYTHON_UNITTEST_MANIFESTS += [
         "tools/python.toml",
     ]
diff --git a/toolkit/crashreporter/mozannotation_client/src/lib.rs b/toolkit/crashreporter/mozannotation_client/src/lib.rs
index df2bd5bf94..2df133c4b9 100644
--- a/toolkit/crashreporter/mozannotation_client/src/lib.rs
+++ b/toolkit/crashreporter/mozannotation_client/src/lib.rs
@@ -101,6 +101,9 @@ extern "C" {
 #[cfg(target_os = "windows")]
 pub const ANNOTATION_SECTION: &'static [u8; 8] = b"mozannot";
 
+#[cfg(target_os = "macos")]
+pub const ANNOTATION_SECTION: &'static [u8; 16] = b"mozannotation\0\0\0";
+
 // TODO: Use the following constants in the assembly below when constant
 // expressions are stabilized: https://github.com/rust-lang/rust/issues/93332
 #[cfg(any(target_os = "linux", target_os = "android"))]
diff --git a/toolkit/crashreporter/mozannotation_server/Cargo.toml b/toolkit/crashreporter/mozannotation_server/Cargo.toml
index 3a5834a645..bd3fb283bf 100644
--- a/toolkit/crashreporter/mozannotation_server/Cargo.toml
+++ b/toolkit/crashreporter/mozannotation_server/Cargo.toml
@@ -8,17 +8,10 @@ license = "MPL-2.0"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-goblin = { version = "0.7", features = ["elf32", "elf64", "pe32", "pe64"] }
-memoffset = "0.8"
 mozannotation_client = { path = "../mozannotation_client/" }
+process_reader = { path = "../process_reader/" }
 thin-vec = { version = "0.2.7", features = ["gecko-ffi"] }
 thiserror = "1.0.38"
 
 [target."cfg(any(target_os = \"linux\", target_os = \"android\"))".dependencies]
-libc = "0.2"
-
-[target."cfg(target_os = \"windows\")".dependencies]
-winapi = { version = "0.3", features = ["minwindef", "memoryapi", "psapi"] }
-
-[target."cfg(target_os = \"macos\")".dependencies]
-mach2 = { version = "0.4" }
+memoffset = "0.8"
diff --git a/toolkit/crashreporter/mozannotation_server/src/errors.rs b/toolkit/crashreporter/mozannotation_server/src/errors.rs
index 037d432e5e..b8103ad4e4 100644
--- a/toolkit/crashreporter/mozannotation_server/src/errors.rs
+++ b/toolkit/crashreporter/mozannotation_server/src/errors.rs
@@ -5,77 +5,13 @@
 use thiserror::Error;
 
 #[derive(Debug, Error)]
-pub enum RetrievalError {
-    #[error("The process handle/PID was invalid")]
-    InvalidProcessHandle,
-    #[error("Could not find the address of the annotations vector")]
-    AnnotationTableNotFound(#[from] FindAnnotationsAddressError),
+pub enum AnnotationsRetrievalError {
+    #[error("Address was out of bounds")]
+    InvalidAddress,
     #[error("Corrupt or wrong annotation table")]
     InvalidAnnotationTable,
     #[error("The data read from the target process is invalid")]
     InvalidData,
-    #[cfg(any(target_os = "linux", target_os = "android"))]
-    #[error("Could not attach to the target process")]
-    AttachError(#[from] PtraceError),
-    #[error("Could not read from the target process address space")]
-    ReadFromProcessError(#[from] ReadError),
-    #[error("waitpid() failed when attaching to the process")]
-    WaitPidError,
-}
-
-#[derive(Debug, Error)]
-pub enum FindAnnotationsAddressError {
-    #[error("Could not convert address {0}")]
-    ConvertAddressError(#[from] std::num::TryFromIntError),
-    #[error("goblin failed to parse a module")]
-    GoblinError(#[from] goblin::error::Error),
-    #[error("Address was out of bounds")]
-    InvalidAddress,
-    #[error("IO error for file {0}")]
-    IOError(#[from] std::io::Error),
-    #[error("Could not find the address of the annotations vector")]
-    NotFound,
-    #[error("Could not parse address {0}")]
-    ParseAddressError(#[from] std::num::ParseIntError),
-    #[error("Could not parse a line in /proc/<pid>/maps")]
-    ProcMapsParseError,
-    #[cfg(any(target_os = "linux", target_os = "android"))]
-    #[error("Program header was not found")]
-    ProgramHeaderNotFound,
-    #[cfg(target_os = "windows")]
-    #[error("Section was not found")]
-    SectionNotFound,
-    #[cfg(target_os = "windows")]
-    #[error("Cannot enumerate the target process's modules")]
-    EnumProcessModulesError,
-    #[error("Could not read memory from the target process")]
-    ReadError(#[from] ReadError),
-    #[cfg(target_os = "macos")]
-    #[error("Failure when requesting the task information")]
-    TaskInfoError,
-    #[cfg(target_os = "macos")]
-    #[error("The task dyld information format is unknown or invalid")]
-    ImageFormatError,
-}
-
-#[derive(Debug, Error)]
-pub enum ReadError {
-    #[cfg(any(target_os = "linux", target_os = "android"))]
-    #[error("ptrace-specific error")]
-    PtraceError(#[from] PtraceError),
-    #[cfg(target_os = "windows")]
-    #[error("ReadProcessMemory failed")]
-    ReadProcessMemoryError,
-    #[cfg(target_os = "macos")]
-    #[error("mach call failed")]
-    MachError,
-}
-
-#[cfg(any(target_os = "linux", target_os = "android"))]
-#[derive(Debug, Error)]
-pub enum PtraceError {
-    #[error("Could not read from the target process address space")]
-    ReadError(#[source] std::io::Error),
-    #[error("Could not trace the process")]
-    TraceError(#[source] std::io::Error),
+    #[error("Could not execute operation on the target process")]
+    ProcessReaderError(#[from] process_reader::error::ProcessReaderError),
 }
diff --git a/toolkit/crashreporter/mozannotation_server/src/lib.rs b/toolkit/crashreporter/mozannotation_server/src/lib.rs
index 6ed5b3cc41..27682247f8 100644
--- a/toolkit/crashreporter/mozannotation_server/src/lib.rs
+++ b/toolkit/crashreporter/mozannotation_server/src/lib.rs
@@ -3,12 +3,18 @@
  * You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 mod errors;
-mod process_reader;
 
 use crate::errors::*;
+#[cfg(any(target_os = "linux", target_os = "android"))]
+use memoffset::offset_of;
+use process_reader::error::ProcessReaderError;
 use process_reader::ProcessReader;
 
+#[cfg(any(target_os = "windows", target_os = "macos"))]
+use mozannotation_client::ANNOTATION_SECTION;
 use mozannotation_client::{Annotation, AnnotationContents, AnnotationMutex};
+#[cfg(any(target_os = "linux", target_os = "android"))]
+use mozannotation_client::{MozAnnotationNote, ANNOTATION_TYPE};
 use std::cmp::min;
 use std::iter::FromIterator;
 use std::mem::{size_of, ManuallyDrop};
@@ -29,12 +35,7 @@ pub struct CAnnotation {
     data: AnnotationData,
 }
 
-#[cfg(target_os = "windows")]
-type ProcessHandle = winapi::shared::ntdef::HANDLE;
-#[cfg(any(target_os = "linux", target_os = "android"))]
-type ProcessHandle = libc::pid_t;
-#[cfg(any(target_os = "macos"))]
-type ProcessHandle = mach2::mach_types::task_t;
+pub type ProcessHandle = process_reader::ProcessHandle;
 
 /// Return the annotations of a given process.
 ///
@@ -68,19 +69,23 @@ pub unsafe extern "C" fn mozannotation_free(ptr: *mut ThinVec<CAnnotation>) {
 pub fn retrieve_annotations(
     process: ProcessHandle,
     max_annotations: usize,
-) -> Result<Box<ThinVec<CAnnotation>>, RetrievalError> {
+) -> Result<Box<ThinVec<CAnnotation>>, AnnotationsRetrievalError> {
     let reader = ProcessReader::new(process)?;
-    let address = reader.find_annotations()?;
+    let address = find_annotations(&reader)?;
 
-    let mut mutex = reader.copy_object_shallow::<AnnotationMutex>(address)?;
+    let mut mutex = reader
+        .copy_object_shallow::<AnnotationMutex>(address)
+        .map_err(ProcessReaderError::from)?;
     let mutex = unsafe { mutex.assume_init_mut() };
 
     // TODO: we should clear the poison value here before getting the mutex
     // contents. Right now we have to fail if the mutex was poisoned.
-    let annotation_table = mutex.get_mut().map_err(|_e| RetrievalError::InvalidData)?;
+    let annotation_table = mutex
+        .get_mut()
+        .map_err(|_e| AnnotationsRetrievalError::InvalidData)?;
 
     if !annotation_table.verify() {
-        return Err(RetrievalError::InvalidAnnotationTable);
+        return Err(AnnotationsRetrievalError::InvalidAnnotationTable);
     }
 
     let vec_pointer = annotation_table.get_ptr();
@@ -97,8 +102,47 @@ pub fn retrieve_annotations(
     Ok(Box::new(annotations))
 }
 
+fn find_annotations(reader: &ProcessReader) -> Result<usize, AnnotationsRetrievalError> {
+    #[cfg(any(target_os = "linux", target_os = "android"))]
+    {
+        let libxul_address = reader.find_module("libxul.so")?;
+        let note_address = reader.find_program_note(
+            libxul_address,
+            ANNOTATION_TYPE,
+            size_of::<MozAnnotationNote>(),
+        )?;
+
+        let note = reader
+            .copy_object::<MozAnnotationNote>(note_address)
+            .map_err(ProcessReaderError::from)?;
+        let desc = note.desc;
+        let ehdr = (-note.ehdr) as usize;
+        let offset = desc + ehdr
+            - (offset_of!(MozAnnotationNote, ehdr) - offset_of!(MozAnnotationNote, desc));
+
+        usize::checked_add(libxul_address, offset).ok_or(AnnotationsRetrievalError::InvalidAddress)
+    }
+    #[cfg(any(target_os = "macos"))]
+    {
+        let libxul_address = reader.find_module("XUL")?;
+        reader
+            .find_section(libxul_address, ANNOTATION_SECTION)
+            .map_err(AnnotationsRetrievalError::from)
+    }
+    #[cfg(any(target_os = "windows"))]
+    {
+        let libxul_address = reader.find_module("xul.dll")?;
+        reader
+            .find_section(libxul_address, ANNOTATION_SECTION)
+            .map_err(AnnotationsRetrievalError::from)
+    }
+}
+
 // Read an annotation from the given address
-fn read_annotation(reader: &ProcessReader, address: usize) -> Result<CAnnotation, ReadError> {
+fn read_annotation(
+    reader: &ProcessReader,
+    address: usize,
+) -> Result<CAnnotation, process_reader::error::ReadError> {
     let raw_annotation = ManuallyDrop::new(reader.copy_object::<Annotation>(address)?);
     let mut annotation = CAnnotation {
         id: raw_annotation.id,
@@ -116,16 +160,16 @@ fn read_annotation(reader: &ProcessReader, address: usize) -> Result<CAnnotation
             annotation.data = AnnotationData::ByteBuffer(string);
         }
         AnnotationContents::CStringPointer => {
-            let buffer = copy_null_terminated_string_pointer(reader, raw_annotation.address)?;
-            annotation.data = AnnotationData::ByteBuffer(buffer);
+            let string = copy_null_terminated_string_pointer(reader, raw_annotation.address)?;
+            annotation.data = AnnotationData::ByteBuffer(string);
         }
         AnnotationContents::CString => {
-            let buffer = copy_null_terminated_string(reader, raw_annotation.address)?;
-            annotation.data = AnnotationData::ByteBuffer(buffer);
+            let string = copy_null_terminated_string(reader, raw_annotation.address)?;
+            annotation.data = AnnotationData::ByteBuffer(string);
         }
         AnnotationContents::ByteBuffer(size) | AnnotationContents::OwnedByteBuffer(size) => {
-            let buffer = copy_bytebuffer(reader, raw_annotation.address, size)?;
-            annotation.data = AnnotationData::ByteBuffer(buffer);
+            let string = copy_bytebuffer(reader, raw_annotation.address, size)?;
+            annotation.data = AnnotationData::ByteBuffer(string);
         }
     };
 
@@ -135,7 +179,7 @@ fn read_annotation(reader: &ProcessReader, address: usize) -> Result<CAnnotation
 fn copy_null_terminated_string_pointer(
     reader: &ProcessReader,
     address: usize,
-) -> Result<ThinVec<u8>, ReadError> {
+) -> Result<ThinVec<u8>, process_reader::error::ReadError> {
     let buffer_address = reader.copy_object::<usize>(address)?;
     copy_null_terminated_string(reader, buffer_address)
 }
@@ -143,56 +187,15 @@ fn copy_null_terminated_string_pointer(
 fn copy_null_terminated_string(
     reader: &ProcessReader,
     address: usize,
-) -> Result<ThinVec<u8>, ReadError> {
-    // Try copying the string word-by-word first, this is considerably faster
-    // than one byte at a time.
-    if let Ok(string) = copy_null_terminated_string_word_by_word(reader, address) {
-        return Ok(string);
-    }
-
-    // Reading the string one word at a time failed, let's try again one byte
-    // at a time. It's slow but it might work in situations where the string
-    // alignment causes word-by-word access to straddle page boundaries.
-    let mut length = 0;
-    let mut string = ThinVec::<u8>::new();
-
-    loop {
-        let char = reader.copy_object::<u8>(address + length)?;
-        length += 1;
-        string.push(char);
-
-        if char == 0 {
-            break;
-        }
-    }
-
-    Ok(string)
+) -> Result<ThinVec<u8>, process_reader::error::ReadError> {
+    let string = reader.copy_null_terminated_string(address)?;
+    Ok(ThinVec::<u8>::from(string.as_bytes()))
 }
 
-fn copy_null_terminated_string_word_by_word(
+fn copy_nscstring(
     reader: &ProcessReader,
     address: usize,
-) -> Result<ThinVec<u8>, ReadError> {
-    const WORD_SIZE: usize = size_of::<usize>();
-    let mut length = 0;
-    let mut string = ThinVec::<u8>::new();
-
-    loop {
-        let array = reader.copy_array::<u8>(address + length, WORD_SIZE)?;
-        let null_terminator = array.iter().position(|&e| e == 0);
-        length += null_terminator.unwrap_or(WORD_SIZE);
-        string.extend(array.into_iter());
-
-        if null_terminator.is_some() {
-            string.truncate(length);
-            break;
-        }
-    }
-
-    Ok(string)
-}
-
-fn copy_nscstring(reader: &ProcessReader, address: usize) -> Result<ThinVec<u8>, ReadError> {
+) -> Result<ThinVec<u8>, process_reader::error::ReadError> {
     // HACK: This assumes the layout of the nsCString object
     let length_address = address + size_of::<usize>();
     let length = reader.copy_object::<u32>(length_address)?;
@@ -211,7 +214,7 @@ fn copy_bytebuffer(
     reader: &ProcessReader,
     address: usize,
     size: u32,
-) -> Result<ThinVec<u8>, ReadError> {
+) -> Result<ThinVec<u8>, process_reader::error::ReadError> {
     let value = reader.copy_array::<u8>(address, size as _)?;
     Ok(ThinVec::<u8>::from_iter(value.into_iter()))
 }
diff --git a/toolkit/crashreporter/mozannotation_server/src/process_reader/windows.rs b/toolkit/crashreporter/mozannotation_server/src/process_reader/windows.rs
deleted file mode 100644
index ffdcd95937..0000000000
--- a/toolkit/crashreporter/mozannotation_server/src/process_reader/windows.rs
+++ /dev/null
@@ -1,193 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
-
-use std::{
-    convert::TryInto,
-    mem::{size_of, MaybeUninit},
-    ptr::null_mut,
-};
-
-use winapi::{
-    shared::{
-        basetsd::SIZE_T,
-        minwindef::{DWORD, FALSE, HMODULE},
-    },
-    um::{
-        memoryapi::ReadProcessMemory,
-        psapi::{K32EnumProcessModules, K32GetModuleInformation, MODULEINFO},
-    },
-};
-
-use crate::{
-    errors::{FindAnnotationsAddressError, ReadError, RetrievalError},
-    ProcessHandle,
-};
-
-use super::ProcessReader;
-
-impl ProcessReader {
-    pub fn new(process: ProcessHandle) -> Result<ProcessReader, RetrievalError> {
-        Ok(ProcessReader { process })
-    }
-
-    pub fn find_annotations(&self) -> Result<usize, FindAnnotationsAddressError> {
-        let modules = self.get_module_list()?;
-
-        modules
-            .iter()
-            .find_map(|&module| {
-                self.get_module_info(module).and_then(|info| {
-                    self.find_annotations_in_module(
-                        info.lpBaseOfDll as usize,
-                        info.SizeOfImage as usize,
-                    )
-                    .ok()
-                })
-            })
-            .ok_or(FindAnnotationsAddressError::InvalidAddress)
-    }
-
-    fn get_module_list(&self) -> Result<Vec<HMODULE>, FindAnnotationsAddressError> {
-        let mut module_num: usize = 100;
-        let mut required_buffer_size: DWORD = 0;
-        let mut module_array = Vec::<MaybeUninit<HMODULE>>::with_capacity(module_num);
-
-        loop {
-            let buffer_size: DWORD = (module_num * size_of::<HMODULE>()).try_into()?;
-            let res = unsafe {
-                K32EnumProcessModules(
-                    self.process,
-                    module_array.as_mut_ptr() as *mut _,
-                    buffer_size,
-                    &mut required_buffer_size as *mut _,
-                )
-            };
-
-            module_num = required_buffer_size as usize / size_of::<HMODULE>();
-
-            if res == 0 {
-                if required_buffer_size > buffer_size {
-                    module_array = Vec::<MaybeUninit<HMODULE>>::with_capacity(module_num);
-                } else {
-                    return Err(FindAnnotationsAddressError::EnumProcessModulesError);
-                }
-            } else {
-                break;
-            }
-        }
-
-        // SAFETY: module_array has been filled by K32EnumProcessModules()
-        let module_array: Vec<HMODULE> = unsafe {
-            module_array.set_len(module_num);
-            std::mem::transmute(module_array)
-        };
-
-        Ok(module_array)
-    }
-
-    fn get_module_info(&self, module: HMODULE) -> Option<MODULEINFO> {
-        let mut info: MaybeUninit<MODULEINFO> = MaybeUninit::uninit();
-        let res = unsafe {
-            K32GetModuleInformation(
-                self.process,
-                module,
-                info.as_mut_ptr(),
-                size_of::<MODULEINFO>() as DWORD,
-            )
-        };
-
-        if res == 0 {
-            None
-        } else {
-            let info = unsafe { info.assume_init() };
-            Some(info)
-        }
-    }
-
-    fn find_annotations_in_module(
-        &self,
-        module_address: usize,
-        size: usize,
-    ) -> Result<usize, FindAnnotationsAddressError> {
-        // We read only the first page from the module, this should be more than
-        // enough to read the header and section list. In the future we might do
-        // this incrementally but for now goblin requires an array to parse
-        // so we can't do it just yet.
-        let page_size = 4096;
-        if size < page_size {
-            // Don't try to read from the target module if it's too small
-            return Err(FindAnnotationsAddressError::ReadError(
-                ReadError::ReadProcessMemoryError,
-            ));
-        }
-
-        let bytes = self.copy_array(module_address as _, 4096)?;
-        let header = goblin::pe::header::Header::parse(&bytes)?;
-
-        // Skip the PE header so we can parse the sections
-        let optional_header_offset = header.dos_header.pe_pointer as usize
-            + goblin::pe::header::SIZEOF_PE_MAGIC
-            + goblin::pe::header::SIZEOF_COFF_HEADER;
-        let offset =
-            &mut (optional_header_offset + header.coff_header.size_of_optional_header as usize);
-
-        let sections = header.coff_header.sections(&bytes, offset)?;
-
-        for section in sections {
-            if section.name.eq(mozannotation_client::ANNOTATION_SECTION) {
-                let address = module_address.checked_add(section.virtual_address as usize);
-                return address.ok_or(FindAnnotationsAddressError::InvalidAddress);
-            }
-        }
-
-        Err(FindAnnotationsAddressError::SectionNotFound)
-    }
-
-    pub fn copy_object_shallow<T>(&self, src: usize) -> Result<MaybeUninit<T>, ReadError> {
-        let mut object = MaybeUninit::<T>::uninit();
-        let res = unsafe {
-            ReadProcessMemory(
-                self.process,
-                src as _,
-                object.as_mut_ptr() as _,
-                size_of::<T>() as SIZE_T,
-                null_mut(),
-            )
-        };
-
-        if res != FALSE {
-            Ok(object)
-        } else {
-            Err(ReadError::ReadProcessMemoryError)
-        }
-    }
-
-    pub fn copy_object<T>(&self, src: usize) -> Result<T, ReadError> {
-        let object = self.copy_object_shallow(src)?;
-        Ok(unsafe { object.assume_init() })
-    }
-
-    pub fn copy_array<T>(&self, src: usize, num: usize) -> Result<Vec<T>, ReadError> {
-        let num_of_bytes = num * size_of::<T>();
-        let mut array: Vec<MaybeUninit<T>> = Vec::with_capacity(num);
-        let res = unsafe {
-            ReadProcessMemory(
-                self.process,
-                src as _,
-                array.as_mut_ptr() as _,
-                num_of_bytes as SIZE_T,
-                null_mut(),
-            )
-        };
-
-        if res != FALSE {
-            unsafe {
-                array.set_len(num);
-                Ok(std::mem::transmute(array))
-            }
-        } else {
-            Err(ReadError::ReadProcessMemoryError)
-        }
-    }
-}
diff --git a/toolkit/crashreporter/mozwer-rust/Cargo.toml b/toolkit/crashreporter/mozwer-rust/Cargo.toml
index 561a10b015..89cf3d4356 100644
--- a/toolkit/crashreporter/mozwer-rust/Cargo.toml
+++ b/toolkit/crashreporter/mozwer-rust/Cargo.toml
@@ -7,7 +7,9 @@ license = "MPL-2.0"
 
 [dependencies]
 libc = "0.2.0"
-mozilla-central-workspace-hack = { version = "0.1", features = ["mozwer_s"], optional = true }
+mozilla-central-workspace-hack = { version = "0.1", features = [
+    "mozwer_s",
+], optional = true }
 process_reader = { path = "../process_reader/" }
 rust-ini = "0.10"
 serde = { version = "1.0", features = ["derive"] }
@@ -23,6 +25,7 @@ features = [
     "Win32_System_Com",
     "Win32_System_Diagnostics_Debug",
     "Win32_System_ErrorReporting",
+    "Win32_System_Memory",
     "Win32_System_ProcessStatus",
     "Win32_System_SystemInformation",
     "Win32_System_SystemServices",
diff --git a/toolkit/crashreporter/mozwer-rust/lib.rs b/toolkit/crashreporter/mozwer-rust/lib.rs
index 198a14a34b..61fc894462 100644
--- a/toolkit/crashreporter/mozwer-rust/lib.rs
+++ b/toolkit/crashreporter/mozwer-rust/lib.rs
@@ -9,7 +9,7 @@ use serde::Serialize;
 use serde_json::ser::to_writer;
 use std::convert::TryInto;
 use std::ffi::{c_void, OsString};
-use std::fs::{read_to_string, DirBuilder, File};
+use std::fs::{read_to_string, DirBuilder, File, OpenOptions};
 use std::io::{BufRead, BufReader, Write};
 use std::mem::{size_of, transmute, zeroed};
 use std::os::windows::ffi::{OsStrExt, OsStringExt};
@@ -248,8 +248,9 @@ fn handle_main_process_crash(
 fn handle_child_process_crash(crash_report: CrashReport, child_process: HANDLE) -> Result<()> {
     let parent_process = get_parent_process(child_process)?;
     let process_reader = ProcessReader::new(parent_process).map_err(|_e| ())?;
+    let libxul_address = process_reader.find_module("xul.dll").map_err(|_e| ())?;
     let wer_notify_proc = process_reader
-        .find_section("xul.dll", "mozwerpt")
+        .find_section(libxul_address, b"mozwerpt")
         .map_err(|_e| ())?;
     let wer_notify_proc = unsafe { transmute::<_, LPTHREAD_START_ROUTINE>(wer_notify_proc) };
 
@@ -524,8 +525,7 @@ impl ApplicationInformation {
         let install_time = ApplicationInformation::get_install_time(
             &crash_reports_dir,
             &application_data.build_id,
-        )
-        .unwrap_or("0".to_string());
+        );
 
         Ok(ApplicationInformation {
             install_path,
@@ -596,10 +596,29 @@ impl ApplicationInformation {
         }
     }
 
-    fn get_install_time(crash_reports_path: &Path, build_id: &str) -> Result<String> {
+    fn get_install_time(crash_reports_path: &Path, build_id: &str) -> String {
         let file_name = "InstallTime".to_owned() + build_id;
         let file_path = crash_reports_path.join(file_name);
-        read_to_string(file_path).map_err(|_e| ())
+
+        // If the file isn't present we'll attempt to atomically create it and
+        // populate it. This code essentially matches the corresponding code in
+        // nsExceptionHandler.cpp SetupExtraData().
+        if let Ok(mut file) = OpenOptions::new()
+            .create_new(true)
+            .write(true)
+            .open(&file_path)
+        {
+            // SAFETY: No risks in calling `time()` with a null pointer.
+            let _ = write!(&mut file, "{}", unsafe { time(null_mut()) }.to_string());
+        }
+
+        // As a last resort, if we can't read the file we fall back to the
+        // current time. This might cause us to overstate the number of users
+        // affected by a crash, but given it's very unlikely to hit this particular
+        // path it won't be a problem.
+        //
+        // SAFETY: No risks in calling `time()` with a null pointer.
+        read_to_string(&file_path).unwrap_or(unsafe { time(null_mut()) }.to_string())
     }
 }
 
diff --git a/toolkit/crashreporter/mozwer/moz.build b/toolkit/crashreporter/mozwer/moz.build
index 1f6418fd48..41aed9b59b 100644
--- a/toolkit/crashreporter/mozwer/moz.build
+++ b/toolkit/crashreporter/mozwer/moz.build
@@ -10,6 +10,13 @@ OS_LIBS += [
     "advapi32",
     "bcrypt",
 ]
+# Version string comparison is generally wrong, but by the time it would
+# actually matter, either bug 1489995 would be fixed, or the build would
+# require version >= 1.78.
+if CONFIG["RUSTC_VERSION"] and CONFIG["RUSTC_VERSION"] >= "1.78.0":
+    OS_LIBS += [
+        "synchronization",
+    ]
 
 DEFFILE = "mozwer.def"
 USE_STATIC_LIBS = True
diff --git a/toolkit/crashreporter/nsExceptionHandler.cpp b/toolkit/crashreporter/nsExceptionHandler.cpp
index aca266749a..868005a5c7 100644
--- a/toolkit/crashreporter/nsExceptionHandler.cpp
+++ b/toolkit/crashreporter/nsExceptionHandler.cpp
@@ -7,6 +7,7 @@
 #include "nsExceptionHandler.h"
 #include "nsExceptionHandlerUtils.h"
 
+#include "json/json.h"
 #include "nsAppDirectoryServiceDefs.h"
 #include "nsComponentManagerUtils.h"
 #include "nsDirectoryServiceDefs.h"
@@ -95,6 +96,9 @@
 using mozilla::InjectCrashRunnable;
 #endif
 
+#include <fstream>
+#include <optional>
+
 #include <stdlib.h>
 #include <time.h>
 #include <prenv.h>
@@ -195,7 +199,7 @@ static const XP_CHAR dumpFileExtension[] = XP_TEXT(".dmp");
 
 static const XP_CHAR extraFileExtension[] = XP_TEXT(".extra");
 static const XP_CHAR memoryReportExtension[] = XP_TEXT(".memory.json.gz");
-static xpstring* defaultMemoryReportPath = nullptr;
+static std::optional<xpstring> defaultMemoryReportPath = {};
 
 static const char kCrashMainID[] = "crash.main.3\n";
 
@@ -433,26 +437,26 @@ static void CreateFileFromPath(const xpstring& path, nsIFile** file) {
   NS_NewLocalFile(nsDependentString(path.c_str()), false, file);
 }
 
-static xpstring* CreatePathFromFile(nsIFile* file) {
+static std::optional<xpstring> CreatePathFromFile(nsIFile* file) {
   nsAutoString path;
   nsresult rv = file->GetPath(path);
   if (NS_FAILED(rv)) {
-    return nullptr;
+    return {};
   }
-  return new xpstring(static_cast<wchar_t*>(path.get()), path.Length());
+  return xpstring(static_cast<wchar_t*>(path.get()), path.Length());
 }
 #else
 static void CreateFileFromPath(const xpstring& path, nsIFile** file) {
   NS_NewNativeLocalFile(nsDependentCString(path.c_str()), false, file);
 }
 
-MAYBE_UNUSED static xpstring* CreatePathFromFile(nsIFile* file) {
+MAYBE_UNUSED static std::optional<xpstring> CreatePathFromFile(nsIFile* file) {
   nsAutoCString path;
   nsresult rv = file->GetNativePath(path);
   if (NS_FAILED(rv)) {
-    return nullptr;
+    return {};
   }
-  return new xpstring(path.get(), path.Length());
+  return xpstring(path.get(), path.Length());
 }
 #endif
 
@@ -2252,7 +2256,7 @@ static nsresult SetupCrashReporterDirectory(nsIFile* aAppDataDirectory,
   NS_ENSURE_SUCCESS(rv, rv);
 
   EnsureDirectoryExists(directory);
-  xpstring* directoryPath = CreatePathFromFile(directory);
+  std::optional<xpstring> directoryPath = CreatePathFromFile(directory);
 
   if (!directoryPath) {
     return NS_ERROR_FAILURE;
@@ -2264,8 +2268,6 @@ static nsresult SetupCrashReporterDirectory(nsIFile* aAppDataDirectory,
   setenv(aEnvVarName, directoryPath->c_str(), /* overwrite */ 1);
 #endif
 
-  delete directoryPath;
-
   if (aDirectory) {
     directory.forget(aDirectory);
   }
@@ -2760,177 +2762,54 @@ nsresult AppendObjCExceptionInfoToAppNotes(void* inException) {
  */
 static nsresult PrefSubmitReports(bool* aSubmitReports, bool writePref) {
   nsresult rv;
-#if defined(XP_WIN)
+#if defined(XP_WIN) || defined(XP_MACOSX) || defined(XP_UNIX)
   /*
-   * NOTE! This needs to stay in sync with the preference checking code
-   *       in toolkit/crashreporter/client/crashreporter_win.cpp
+   * NOTE! This needs to stay in sync with the code in
+   * toolkit/crashreporter/client/app/src/{logic,settings}.rs
    */
-  nsCOMPtr<nsIXULAppInfo> appinfo =
-      do_GetService("@mozilla.org/xre/app-info;1", &rv);
-  NS_ENSURE_SUCCESS(rv, rv);
-
-  nsAutoCString appVendor, appName;
-  rv = appinfo->GetVendor(appVendor);
-  NS_ENSURE_SUCCESS(rv, rv);
-  rv = appinfo->GetName(appName);
+  nsCOMPtr<nsIFile> reporterSettings;
+  rv = NS_GetSpecialDirectory("UAppData", getter_AddRefs(reporterSettings));
   NS_ENSURE_SUCCESS(rv, rv);
+  reporterSettings->AppendNative("Crash Reports"_ns);
+  reporterSettings->AppendNative("crashreporter_settings.json"_ns);
 
-  nsCOMPtr<nsIWindowsRegKey> regKey(
-      do_CreateInstance("@mozilla.org/windows-registry-key;1", &rv));
-  NS_ENSURE_SUCCESS(rv, rv);
-
-  nsAutoCString regPath;
-
-  regPath.AppendLiteral("Software\\");
-
-  // We need to ensure the registry keys are created so we can properly
-  // write values to it
-
-  // Create appVendor key
-  if (!appVendor.IsEmpty()) {
-    regPath.Append(appVendor);
-    regKey->Create(nsIWindowsRegKey::ROOT_KEY_CURRENT_USER,
-                   NS_ConvertUTF8toUTF16(regPath),
-                   nsIWindowsRegKey::ACCESS_SET_VALUE);
-    regPath.Append('\\');
-  }
-
-  // Create appName key
-  regPath.Append(appName);
-  regKey->Create(nsIWindowsRegKey::ROOT_KEY_CURRENT_USER,
-                 NS_ConvertUTF8toUTF16(regPath),
-                 nsIWindowsRegKey::ACCESS_SET_VALUE);
-  regPath.Append('\\');
-
-  // Create Crash Reporter key
-  regPath.AppendLiteral("Crash Reporter");
-  regKey->Create(nsIWindowsRegKey::ROOT_KEY_CURRENT_USER,
-                 NS_ConvertUTF8toUTF16(regPath),
-                 nsIWindowsRegKey::ACCESS_SET_VALUE);
-
-  // If we're saving the pref value, just write it to ROOT_KEY_CURRENT_USER
-  // and we're done.
-  if (writePref) {
-    rv = regKey->Open(nsIWindowsRegKey::ROOT_KEY_CURRENT_USER,
-                      NS_ConvertUTF8toUTF16(regPath),
-                      nsIWindowsRegKey::ACCESS_SET_VALUE);
-    NS_ENSURE_SUCCESS(rv, rv);
-
-    uint32_t value = *aSubmitReports ? 1 : 0;
-    rv = regKey->WriteIntValue(u"SubmitCrashReport"_ns, value);
-    regKey->Close();
-    return rv;
-  }
-
-  // We're reading the pref value, so we need to first look under
-  // ROOT_KEY_LOCAL_MACHINE to see if it's set there, and then fall back to
-  // ROOT_KEY_CURRENT_USER. If it's not set in either place, the pref defaults
-  // to "true".
-  uint32_t value;
-  rv = regKey->Open(nsIWindowsRegKey::ROOT_KEY_LOCAL_MACHINE,
-                    NS_ConvertUTF8toUTF16(regPath),
-                    nsIWindowsRegKey::ACCESS_QUERY_VALUE);
-  if (NS_SUCCEEDED(rv)) {
-    rv = regKey->ReadIntValue(u"SubmitCrashReport"_ns, &value);
-    regKey->Close();
-    if (NS_SUCCEEDED(rv)) {
-      *aSubmitReports = !!value;
-      return NS_OK;
-    }
-  }
-
-  rv = regKey->Open(nsIWindowsRegKey::ROOT_KEY_CURRENT_USER,
-                    NS_ConvertUTF8toUTF16(regPath),
-                    nsIWindowsRegKey::ACCESS_QUERY_VALUE);
-  if (NS_FAILED(rv)) {
-    *aSubmitReports = true;
-    return NS_OK;
-  }
+  std::optional<xpstring> file_path = CreatePathFromFile(reporterSettings);
 
-  rv = regKey->ReadIntValue(u"SubmitCrashReport"_ns, &value);
-  // default to true on failure
-  if (NS_FAILED(rv)) {
-    value = 1;
-    rv = NS_OK;
+  if (!file_path) {
+    return NS_ERROR_FAILURE;
   }
-  regKey->Close();
 
-  *aSubmitReports = !!value;
-  return NS_OK;
-#elif defined(XP_MACOSX)
-  rv = NS_OK;
-  if (writePref) {
-    CFPropertyListRef cfValue =
-        (CFPropertyListRef)(*aSubmitReports ? kCFBooleanTrue : kCFBooleanFalse);
-    ::CFPreferencesSetAppValue(CFSTR("submitReport"), cfValue,
-                               reporterClientAppID);
-    if (!::CFPreferencesAppSynchronize(reporterClientAppID))
-      rv = NS_ERROR_FAILURE;
-  } else {
-    *aSubmitReports = true;
-    Boolean keyExistsAndHasValidFormat = false;
-    Boolean prefValue = ::CFPreferencesGetAppBooleanValue(
-        CFSTR("submitReport"), reporterClientAppID,
-        &keyExistsAndHasValidFormat);
-    if (keyExistsAndHasValidFormat) *aSubmitReports = !!prefValue;
-  }
-  return rv;
-#elif defined(XP_UNIX)
-  /*
-   * NOTE! This needs to stay in sync with the preference checking code
-   *       in toolkit/crashreporter/client/crashreporter_linux.cpp
-   */
-  nsCOMPtr<nsIFile> reporterINI;
-  rv = NS_GetSpecialDirectory("UAppData", getter_AddRefs(reporterINI));
-  NS_ENSURE_SUCCESS(rv, rv);
-  reporterINI->AppendNative("Crash Reports"_ns);
-  reporterINI->AppendNative("crashreporter.ini"_ns);
+  Json::Value root;
 
   bool exists;
-  rv = reporterINI->Exists(&exists);
+  rv = reporterSettings->Exists(&exists);
   NS_ENSURE_SUCCESS(rv, rv);
   if (!exists) {
     if (!writePref) {
-      // If reading the pref, default to true if .ini doesn't exist.
+      // If reading the pref, default to true if the settings file doesn't
+      // exist.
       *aSubmitReports = true;
       return NS_OK;
     }
-    // Create the file so the INI processor can write to it.
-    rv = reporterINI->Create(nsIFile::NORMAL_FILE_TYPE, 0600);
+    // Create the file so the JSON processor can write to it.
+    rv = reporterSettings->Create(nsIFile::NORMAL_FILE_TYPE, 0600);
     NS_ENSURE_SUCCESS(rv, rv);
+  } else {
+    // Read the root value
+    std::ifstream file(*file_path);
+    file >> root;
   }
 
-  nsCOMPtr<nsIINIParserFactory> iniFactory =
-      do_GetService("@mozilla.org/xpcom/ini-parser-factory;1", &rv);
-  NS_ENSURE_SUCCESS(rv, rv);
-
-  nsCOMPtr<nsIINIParser> iniParser;
-  rv = iniFactory->CreateINIParser(reporterINI, getter_AddRefs(iniParser));
-  NS_ENSURE_SUCCESS(rv, rv);
-
-  // If we're writing the pref, just set and we're done.
   if (writePref) {
-    nsCOMPtr<nsIINIParserWriter> iniWriter = do_QueryInterface(iniParser);
-    NS_ENSURE_TRUE(iniWriter, NS_ERROR_FAILURE);
-
-    rv = iniWriter->SetString("Crash Reporter"_ns, "SubmitReport"_ns,
-                              *aSubmitReports ? "1"_ns : "0"_ns);
-    NS_ENSURE_SUCCESS(rv, rv);
-    rv = iniWriter->WriteFile(reporterINI);
-    return rv;
-  }
-
-  nsAutoCString submitReportValue;
-  rv = iniParser->GetString("Crash Reporter"_ns, "SubmitReport"_ns,
-                            submitReportValue);
-
-  // Default to "true" if the pref can't be found.
-  if (NS_FAILED(rv))
-    *aSubmitReports = true;
-  else if (submitReportValue.EqualsASCII("0"))
-    *aSubmitReports = false;
-  else
+    root["submit_report"] = *aSubmitReports;
+    std::ofstream file(*file_path);
+    file << root;
+  } else if (root["submit_report"].isBool()) {
+    *aSubmitReports = root["submit_report"].asBool();
+  } else {
+    // Default to "true" if the pref can't be found.
     *aSubmitReports = true;
+  }
 
   return NS_OK;
 #else
@@ -2973,19 +2852,17 @@ static void SetCrashEventsDir(nsIFile* aDir) {
     EnsureDirectoryExists(eventsDir);
   }
 
-  xpstring* path = CreatePathFromFile(eventsDir);
+  std::optional<xpstring> path = CreatePathFromFile(eventsDir);
   if (!path) {
     return;  // There's no clean failure from this
   }
 
-  eventsDirectory = xpstring(*path);
+  eventsDirectory = *path;
 #ifdef XP_WIN
   SetEnvironmentVariableW(eventsDirectoryEnv, path->c_str());
 #else
   setenv(eventsDirectoryEnv, path->c_str(), /* overwrite */ 1);
 #endif
-
-  delete path;
 }
 
 void SetProfileDirectory(nsIFile* aDir) {
diff --git a/toolkit/crashreporter/process_reader/Cargo.toml b/toolkit/crashreporter/process_reader/Cargo.toml
index f84a00a29f..5fb20cf95a 100644
--- a/toolkit/crashreporter/process_reader/Cargo.toml
+++ b/toolkit/crashreporter/process_reader/Cargo.toml
@@ -10,14 +10,18 @@ license = "MPL-2.0"
 [dependencies]
 goblin = { version = "0.7", features = ["elf32", "elf64", "pe32", "pe64"] }
 memoffset = "0.9"
-mozilla-central-workspace-hack = { version = "0.1", optional = true }
 thiserror = "1.0"
 
+[target."cfg(any(target_os = \"linux\", target_os = \"android\"))".dependencies]
+libc = "0.2"
+
 [target."cfg(target_os = \"windows\")".dependencies]
-[dependencies.windows-sys]
-version = "0.52"
-features = [
+windows-sys = { version = "0.52", features = [
     "Win32_Foundation",
     "Win32_System_Diagnostics_Debug",
     "Win32_System_ProcessStatus",
-]
+] }
+mozilla-central-workspace-hack = { version = "0.1", optional = true }
+
+[target."cfg(target_os = \"macos\")".dependencies]
+mach2 = { version = "0.4" }
diff --git a/toolkit/crashreporter/process_reader/src/error.rs b/toolkit/crashreporter/process_reader/src/error.rs
index af4d803a7a..2c681f78fb 100644
--- a/toolkit/crashreporter/process_reader/src/error.rs
+++ b/toolkit/crashreporter/process_reader/src/error.rs
@@ -8,6 +8,8 @@ use thiserror::Error;
 pub enum ProcessReaderError {
     #[error("Could not convert address {0}")]
     ConvertAddressError(#[from] std::num::TryFromIntError),
+    #[error("Could not parse address {0}")]
+    ParseAddressError(#[from] std::num::ParseIntError),
     #[cfg(target_os = "windows")]
     #[error("Cannot enumerate the target process's modules")]
     EnumProcessModulesError,
@@ -17,14 +19,52 @@ pub enum ProcessReaderError {
     InvalidAddress,
     #[error("Could not read from the target process address space")]
     ReadFromProcessError(#[from] ReadError),
-    #[cfg(target_os = "windows")]
+    #[cfg(any(target_os = "windows", target_os = "macos"))]
     #[error("Section was not found")]
     SectionNotFound,
+    #[cfg(any(target_os = "linux", target_os = "android"))]
+    #[error("Could not attach to the target process")]
+    AttachError(#[from] PtraceError),
+    #[cfg(any(target_os = "linux", target_os = "android"))]
+    #[error("Note not found")]
+    NoteNotFound,
+    #[cfg(any(target_os = "linux", target_os = "android"))]
+    #[error("waitpid() failed when attaching to the process")]
+    WaitPidError,
+    #[cfg(any(target_os = "linux", target_os = "android"))]
+    #[error("Could not parse a line in /proc/<pid>/maps")]
+    ProcMapsParseError,
+    #[error("Module not found")]
+    ModuleNotFound,
+    #[cfg(any(target_os = "linux", target_os = "android"))]
+    #[error("IO error for file {0}")]
+    IOError(#[from] std::io::Error),
+    #[cfg(target_os = "macos")]
+    #[error("Failure when requesting the task information")]
+    TaskInfoError,
+    #[cfg(target_os = "macos")]
+    #[error("The task dyld information format is unknown or invalid")]
+    ImageFormatError,
 }
 
 #[derive(Debug, Error)]
 pub enum ReadError {
+    #[cfg(target_os = "macos")]
+    #[error("mach call failed")]
+    MachError,
+    #[cfg(any(target_os = "linux", target_os = "android"))]
+    #[error("ptrace-specific error")]
+    PtraceError(#[from] PtraceError),
     #[cfg(target_os = "windows")]
     #[error("ReadProcessMemory failed")]
     ReadProcessMemoryError,
 }
+
+#[cfg(any(target_os = "linux", target_os = "android"))]
+#[derive(Debug, Error)]
+pub enum PtraceError {
+    #[error("Could not read from the target process address space")]
+    ReadError(#[source] std::io::Error),
+    #[error("Could not trace the process")]
+    TraceError(#[source] std::io::Error),
+}
diff --git a/toolkit/crashreporter/process_reader/src/lib.rs b/toolkit/crashreporter/process_reader/src/lib.rs
index 1189ff144e..09936e46f1 100644
--- a/toolkit/crashreporter/process_reader/src/lib.rs
+++ b/toolkit/crashreporter/process_reader/src/lib.rs
@@ -2,12 +2,78 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
+use std::{ffi::CString, mem::size_of};
+
+use error::ReadError;
+
+pub mod error;
+mod platform;
+
 #[cfg(target_os = "windows")]
-type ProcessHandle = windows_sys::Win32::Foundation::HANDLE;
+pub type ProcessHandle = windows_sys::Win32::Foundation::HANDLE;
+
+#[cfg(any(target_os = "linux", target_os = "android"))]
+pub type ProcessHandle = libc::pid_t;
+
+#[cfg(any(target_os = "macos"))]
+pub type ProcessHandle = mach2::mach_types::task_t;
 
 pub struct ProcessReader {
     process: ProcessHandle,
 }
 
-mod error;
-mod process_reader;
+impl ProcessReader {
+    pub fn copy_null_terminated_string(&self, address: usize) -> Result<CString, ReadError> {
+        // Try copying the string word-by-word first, this is considerably
+        // faster than one byte at a time.
+        if let Ok(string) = self.copy_null_terminated_string_word_by_word(address) {
+            return Ok(string);
+        }
+
+        // Reading the string one word at a time failed, let's try again one
+        // byte at a time. It's slow but it might work in situations where the
+        // string alignment causes word-by-word access to straddle page
+        // boundaries.
+        let mut length = 0;
+        let mut string = Vec::<u8>::new();
+
+        loop {
+            let char = self.copy_object::<u8>(address + length)?;
+            length += 1;
+            string.push(char);
+
+            if char == 0 {
+                break;
+            }
+        }
+
+        // SAFETY: If we reach this point we've read at least one byte and we
+        // know that the last one we read is nul.
+        Ok(unsafe { CString::from_vec_with_nul_unchecked(string) })
+    }
+
+    fn copy_null_terminated_string_word_by_word(
+        &self,
+        address: usize,
+    ) -> Result<CString, ReadError> {
+        const WORD_SIZE: usize = size_of::<usize>();
+        let mut length = 0;
+        let mut string = Vec::<u8>::new();
+
+        loop {
+            let array = self.copy_array::<u8>(address + length, WORD_SIZE)?;
+            let null_terminator = array.iter().position(|&e| e == 0);
+            length += null_terminator.unwrap_or(WORD_SIZE);
+            string.extend(array.into_iter());
+
+            if null_terminator.is_some() {
+                string.truncate(length + 1);
+                break;
+            }
+        }
+
+        // SAFETY: If we reach this point we've read at least one byte and we
+        // know that the last one we read is nul.
+        Ok(unsafe { CString::from_vec_with_nul_unchecked(string) })
+    }
+}
diff --git a/toolkit/crashreporter/mozannotation_server/src/process_reader.rs b/toolkit/crashreporter/process_reader/src/platform.rs
index b405b4b725..0ac354cd66 100644
--- a/toolkit/crashreporter/mozannotation_server/src/process_reader.rs
+++ b/toolkit/crashreporter/process_reader/src/platform.rs
@@ -2,12 +2,6 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
-use crate::ProcessHandle;
-
-pub struct ProcessReader {
-    process: ProcessHandle,
-}
-
 #[cfg(target_os = "windows")]
 mod windows;
 
diff --git a/toolkit/crashreporter/mozannotation_server/src/process_reader/linux.rs b/toolkit/crashreporter/process_reader/src/platform/linux.rs
index 34f8ef90d5..4a87e5480b 100644
--- a/toolkit/crashreporter/mozannotation_server/src/process_reader/linux.rs
+++ b/toolkit/crashreporter/process_reader/src/platform/linux.rs
@@ -2,7 +2,6 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
-use mozannotation_client::MozAnnotationNote;
 use std::{
     cmp::min,
     fs::File,
@@ -13,12 +12,10 @@ use std::{
 };
 
 use crate::{
-    errors::{FindAnnotationsAddressError, PtraceError, ReadError, RetrievalError},
-    ProcessHandle,
+    error::{ProcessReaderError, PtraceError, ReadError},
+    ProcessHandle, ProcessReader,
 };
 
-use super::ProcessReader;
-
 use goblin::elf::{
     self,
     program_header::{PF_R, PT_NOTE},
@@ -28,11 +25,9 @@ use libc::{
     c_int, c_long, c_void, pid_t, ptrace, waitpid, EINTR, PTRACE_ATTACH, PTRACE_DETACH,
     PTRACE_PEEKDATA, __WALL,
 };
-use memoffset::offset_of;
-use mozannotation_client::ANNOTATION_TYPE;
 
 impl ProcessReader {
-    pub fn new(process: ProcessHandle) -> Result<ProcessReader, RetrievalError> {
+    pub fn new(process: ProcessHandle) -> Result<ProcessReader, ProcessReaderError> {
         let pid: pid_t = process;
 
         ptrace_attach(pid)?;
@@ -46,7 +41,7 @@ impl ProcessReader {
                     EINTR => continue,
                     _ => {
                         ptrace_detach(pid)?;
-                        return Err(RetrievalError::WaitPidError);
+                        return Err(ProcessReaderError::WaitPidError);
                     }
                 }
             } else {
@@ -57,73 +52,78 @@ impl ProcessReader {
         Ok(ProcessReader { process: pid })
     }
 
-    pub fn find_annotations(&self) -> Result<usize, FindAnnotationsAddressError> {
+    pub fn find_module(&self, module_name: &str) -> Result<usize, ProcessReaderError> {
         let maps_file = File::open(format!("/proc/{}/maps", self.process))?;
 
         BufReader::new(maps_file)
             .lines()
             .flatten()
-            .find_map(|line| self.find_annotations_in_module(&line).ok())
-            .ok_or(FindAnnotationsAddressError::NotFound)
+            .map(|line| parse_proc_maps_line(&line))
+            .filter_map(Result::ok)
+            .find_map(|(name, address)| {
+                if name.is_some_and(|name| name.eq(module_name)) {
+                    Some(address)
+                } else {
+                    None
+                }
+            })
+            .ok_or(ProcessReaderError::ModuleNotFound)
     }
 
-    fn find_annotations_in_module(&self, line: &str) -> Result<usize, FindAnnotationsAddressError> {
-        parse_proc_maps_line(line).and_then(|module_address| {
-            let header_bytes = self.copy_array(module_address, size_of::<elf::Header>())?;
-            let elf_header = Elf::parse_header(&header_bytes)?;
-
-            let program_header_bytes = self.copy_array(
-                module_address + (elf_header.e_phoff as usize),
-                (elf_header.e_phnum as usize) * (elf_header.e_phentsize as usize),
-            )?;
-
-            let mut elf = Elf::lazy_parse(elf_header)?;
-            let context = goblin::container::Ctx {
-                container: elf.header.container()?,
-                le: elf.header.endianness()?,
-            };
-
-            elf.program_headers = ProgramHeader::parse(
-                &program_header_bytes,
-                0,
-                elf_header.e_phnum as usize,
-                context,
-            )?;
-
-            self.find_mozannotation_note(module_address, &elf)
-                .ok_or(FindAnnotationsAddressError::ProgramHeaderNotFound)
-        })
+    pub fn find_program_note(
+        &self,
+        module_address: usize,
+        note_type: u32,
+        note_size: usize,
+    ) -> Result<usize, ProcessReaderError> {
+        let header_bytes = self.copy_array(module_address, size_of::<elf::Header>())?;
+        let elf_header = Elf::parse_header(&header_bytes)?;
+
+        let program_header_bytes = self.copy_array(
+            module_address + (elf_header.e_phoff as usize),
+            (elf_header.e_phnum as usize) * (elf_header.e_phentsize as usize),
+        )?;
+
+        let mut elf = Elf::lazy_parse(elf_header)?;
+        let context = goblin::container::Ctx {
+            container: elf.header.container()?,
+            le: elf.header.endianness()?,
+        };
+
+        elf.program_headers = ProgramHeader::parse(
+            &program_header_bytes,
+            0,
+            elf_header.e_phnum as usize,
+            context,
+        )?;
+
+        self.find_note_in_headers(&elf, module_address, note_type, note_size)
     }
 
-    // Looks through the program headers for the note contained in the
-    // mozannotation_client crate. If the note is found return the address of the
-    // note's desc field as well as its contents.
-    fn find_mozannotation_note(&self, module_address: usize, elf: &Elf) -> Option<usize> {
+    fn find_note_in_headers(
+        &self,
+        elf: &Elf,
+        address: usize,
+        note_type: u32,
+        note_size: usize,
+    ) -> Result<usize, ProcessReaderError> {
         for program_header in elf.program_headers.iter() {
             // We're looking for a note in the program headers, it needs to be
             // readable and it needs to be at least as large as the
-            // MozAnnotationNote structure.
+            // requested size.
             if (program_header.p_type == PT_NOTE)
                 && ((program_header.p_flags & PF_R) != 0
-                    && (program_header.p_memsz as usize >= size_of::<MozAnnotationNote>()))
+                    && (program_header.p_memsz as usize >= note_size))
             {
                 // Iterate over the notes
-                let notes_address = module_address + program_header.p_offset as usize;
+                let notes_address = address + program_header.p_offset as usize;
                 let mut notes_offset = 0;
                 let notes_size = program_header.p_memsz as usize;
                 while notes_offset < notes_size {
                     let note_address = notes_address + notes_offset;
                     if let Ok(note) = self.copy_object::<goblin::elf::note::Nhdr32>(note_address) {
-                        if note.n_type == ANNOTATION_TYPE {
-                            if let Ok(note) = self.copy_object::<MozAnnotationNote>(note_address) {
-                                let desc = note.desc;
-                                let ehdr = (-note.ehdr) as usize;
-                                let offset = desc + ehdr
-                                    - (offset_of!(MozAnnotationNote, ehdr)
-                                        - offset_of!(MozAnnotationNote, desc));
-
-                                return usize::checked_add(module_address, offset);
-                            }
+                        if note.n_type == note_type {
+                            return Ok(note_address);
                         }
 
                         notes_offset += size_of::<goblin::elf::note::Nhdr32>()
@@ -136,7 +136,7 @@ impl ProcessReader {
             }
         }
 
-        None
+        Err(ProcessReaderError::NoteNotFound)
     }
 
     pub fn copy_object_shallow<T>(&self, src: usize) -> Result<MaybeUninit<T>, ReadError> {
@@ -189,38 +189,46 @@ impl Drop for ProcessReader {
     }
 }
 
-fn parse_proc_maps_line(line: &str) -> Result<usize, FindAnnotationsAddressError> {
+fn parse_proc_maps_line(line: &str) -> Result<(Option<String>, usize), ProcessReaderError> {
     let mut splits = line.trim().splitn(6, ' ');
     let address_str = splits
         .next()
-        .ok_or(FindAnnotationsAddressError::ProcMapsParseError)?;
+        .ok_or(ProcessReaderError::ProcMapsParseError)?;
     let _perms_str = splits
         .next()
-        .ok_or(FindAnnotationsAddressError::ProcMapsParseError)?;
+        .ok_or(ProcessReaderError::ProcMapsParseError)?;
     let _offset_str = splits
         .next()
-        .ok_or(FindAnnotationsAddressError::ProcMapsParseError)?;
+        .ok_or(ProcessReaderError::ProcMapsParseError)?;
     let _dev_str = splits
         .next()
-        .ok_or(FindAnnotationsAddressError::ProcMapsParseError)?;
+        .ok_or(ProcessReaderError::ProcMapsParseError)?;
     let _inode_str = splits
         .next()
-        .ok_or(FindAnnotationsAddressError::ProcMapsParseError)?;
-    let _path_str = splits
+        .ok_or(ProcessReaderError::ProcMapsParseError)?;
+    let path_str = splits
         .next()
-        .ok_or(FindAnnotationsAddressError::ProcMapsParseError)?;
+        .ok_or(ProcessReaderError::ProcMapsParseError)?;
 
     let address = get_proc_maps_address(address_str)?;
 
-    Ok(address)
+    // Note that we don't care if the mapped file has been deleted because
+    // we're reading everything from memory.
+    let name = path_str
+        .trim_end_matches(" (deleted)")
+        .rsplit('/')
+        .next()
+        .map(String::from);
+
+    Ok((name, address))
 }
 
-fn get_proc_maps_address(addresses: &str) -> Result<usize, FindAnnotationsAddressError> {
+fn get_proc_maps_address(addresses: &str) -> Result<usize, ProcessReaderError> {
     let begin = addresses
         .split('-')
         .next()
-        .ok_or(FindAnnotationsAddressError::ProcMapsParseError)?;
-    usize::from_str_radix(begin, 16).map_err(FindAnnotationsAddressError::from)
+        .ok_or(ProcessReaderError::ProcMapsParseError)?;
+    usize::from_str_radix(begin, 16).map_err(ProcessReaderError::from)
 }
 
 fn uninit_as_bytes_mut<T>(elem: &mut MaybeUninit<T>) -> &mut [MaybeUninit<u8>] {
diff --git a/toolkit/crashreporter/mozannotation_server/src/process_reader/macos.rs b/toolkit/crashreporter/process_reader/src/platform/macos.rs
index 52a3957ca9..a0dfa2b8fd 100644
--- a/toolkit/crashreporter/mozannotation_server/src/process_reader/macos.rs
+++ b/toolkit/crashreporter/process_reader/src/platform/macos.rs
@@ -15,12 +15,10 @@ use mach2::{
 use std::mem::{size_of, MaybeUninit};
 
 use crate::{
-    errors::{FindAnnotationsAddressError, ReadError, RetrievalError},
-    ProcessHandle,
+    error::{ProcessReaderError, ReadError},
+    ProcessHandle, ProcessReader,
 };
 
-use super::ProcessReader;
-
 #[repr(C)]
 #[derive(Copy, Clone, Debug)]
 struct AllImagesInfo {
@@ -55,23 +53,22 @@ struct ImageInfo {
 }
 
 const DATA_SEGMENT: &[u8; 16] = b"__DATA\0\0\0\0\0\0\0\0\0\0";
-const MOZANNOTATION_SECTION: &[u8; 16] = b"mozannotation\0\0\0";
 
 impl ProcessReader {
-    pub fn new(process: ProcessHandle) -> Result<ProcessReader, RetrievalError> {
+    pub fn new(process: ProcessHandle) -> Result<ProcessReader, ProcessReaderError> {
         Ok(ProcessReader { process })
     }
 
-    pub fn find_annotations(&self) -> Result<usize, FindAnnotationsAddressError> {
+    pub fn find_module(&self, module_name: &str) -> Result<usize, ProcessReaderError> {
         let dyld_info = self.task_info()?;
         if (dyld_info.all_image_info_format as u32) != TASK_DYLD_ALL_IMAGE_INFO_64 {
-            return Err(FindAnnotationsAddressError::ImageFormatError);
+            return Err(ProcessReaderError::ImageFormatError);
         }
 
         let all_image_info_size = dyld_info.all_image_info_size;
         let all_image_info_addr = dyld_info.all_image_info_addr;
         if (all_image_info_size as usize) < size_of::<AllImagesInfo>() {
-            return Err(FindAnnotationsAddressError::ImageFormatError);
+            return Err(ProcessReaderError::ImageFormatError);
         }
 
         let all_images_info = self.copy_object::<AllImagesInfo>(all_image_info_addr as _)?;
@@ -84,80 +81,94 @@ impl ProcessReader {
 
         images
             .iter()
-            .find_map(|image| self.find_annotations_in_image(image))
-            .ok_or(FindAnnotationsAddressError::NotFound)
-    }
-
-    fn task_info(&self) -> Result<task_dyld_info, FindAnnotationsAddressError> {
-        let mut info = std::mem::MaybeUninit::<task_dyld_info>::uninit();
-        let mut count = (std::mem::size_of::<task_dyld_info>() / std::mem::size_of::<u32>()) as u32;
-
-        let res = unsafe {
-            task_info(
-                self.process,
-                TASK_DYLD_INFO,
-                info.as_mut_ptr().cast(),
-                &mut count,
-            )
-        };
-
-        if res == KERN_SUCCESS {
-            // SAFETY: this will be initialized if the call succeeded
-            unsafe { Ok(info.assume_init()) }
-        } else {
-            Err(FindAnnotationsAddressError::TaskInfoError)
-        }
+            .find(|&image| {
+                let image_path = self.copy_null_terminated_string(image.file_path as usize);
+
+                if let Ok(image_path) = image_path {
+                    if let Some(image_name) = image_path.into_bytes().rsplit(|&b| b == b'/').next()
+                    {
+                        image_name.eq(module_name.as_bytes())
+                    } else {
+                        false
+                    }
+                } else {
+                    false
+                }
+            })
+            .map(|image| image.load_address as usize)
+            .ok_or(ProcessReaderError::ModuleNotFound)
     }
 
-    fn find_annotations_in_image(&self, image: &ImageInfo) -> Option<usize> {
-        self.copy_object::<Header64>(image.load_address as _)
-            .map_err(FindAnnotationsAddressError::from)
-            .and_then(|header| {
-                let image_address = image.load_address as usize;
-                let mut address = image_address + size_of::<Header64>();
-
-                if header.magic == MH_MAGIC_64
-                    && (header.filetype == MH_EXECUTE || header.filetype == MH_DYLIB)
-                {
-                    let end_of_commands = address + (header.sizeofcmds as usize);
-
-                    while address < end_of_commands {
-                        let command = self.copy_object::<LoadCommandHeader>(address)?;
-
-                        if command.cmd == LC_SEGMENT_64 {
-                            if let Ok(offset) = self.find_annotations_in_segment(address) {
-                                return image_address
-                                    .checked_add(offset)
-                                    .ok_or(FindAnnotationsAddressError::InvalidAddress);
-                            }
-                        }
-
-                        address += command.cmdsize as usize;
+    pub fn find_section(
+        &self,
+        module_address: usize,
+        section_name: &[u8; 16],
+    ) -> Result<usize, ProcessReaderError> {
+        let header = self.copy_object::<Header64>(module_address)?;
+        let mut address = module_address + size_of::<Header64>();
+
+        if header.magic == MH_MAGIC_64
+            && (header.filetype == MH_EXECUTE || header.filetype == MH_DYLIB)
+        {
+            let end_of_commands = address + (header.sizeofcmds as usize);
+
+            while address < end_of_commands {
+                let command = self.copy_object::<LoadCommandHeader>(address)?;
+
+                if command.cmd == LC_SEGMENT_64 {
+                    if let Ok(offset) = self.find_section_in_segment(address, section_name) {
+                        return module_address
+                            .checked_add(offset)
+                            .ok_or(ProcessReaderError::InvalidAddress);
                     }
                 }
 
-                Err(FindAnnotationsAddressError::NotFound)
-            })
-            .ok()
+                address += command.cmdsize as usize;
+            }
+        }
+
+        Err(ProcessReaderError::SectionNotFound)
     }
 
-    fn find_annotations_in_segment(
+    fn find_section_in_segment(
         &self,
         segment_address: usize,
-    ) -> Result<usize, FindAnnotationsAddressError> {
+        section_name: &[u8; 16],
+    ) -> Result<usize, ProcessReaderError> {
         let segment = self.copy_object::<SegmentCommand64>(segment_address)?;
 
         if segment.segname.eq(DATA_SEGMENT) {
             let sections_addr = segment_address + size_of::<SegmentCommand64>();
             let sections = self.copy_array::<Section64>(sections_addr, segment.nsects as usize)?;
             for section in &sections {
-                if section.sectname.eq(MOZANNOTATION_SECTION) {
+                if section.sectname.eq(section_name) {
                     return Ok(section.offset as usize);
                 }
             }
         }
 
-        Err(FindAnnotationsAddressError::InvalidAddress)
+        Err(ProcessReaderError::SectionNotFound)
+    }
+
+    fn task_info(&self) -> Result<task_dyld_info, ProcessReaderError> {
+        let mut info = std::mem::MaybeUninit::<task_dyld_info>::uninit();
+        let mut count = (std::mem::size_of::<task_dyld_info>() / std::mem::size_of::<u32>()) as u32;
+
+        let res = unsafe {
+            task_info(
+                self.process,
+                TASK_DYLD_INFO,
+                info.as_mut_ptr().cast(),
+                &mut count,
+            )
+        };
+
+        if res == KERN_SUCCESS {
+            // SAFETY: this will be initialized if the call succeeded
+            unsafe { Ok(info.assume_init()) }
+        } else {
+            Err(ProcessReaderError::TaskInfoError)
+        }
     }
 
     pub fn copy_object_shallow<T>(&self, src: usize) -> Result<MaybeUninit<T>, ReadError> {
diff --git a/toolkit/crashreporter/process_reader/src/process_reader/windows.rs b/toolkit/crashreporter/process_reader/src/platform/windows.rs
index 1dd1a13049..2d8c63444e 100644
--- a/toolkit/crashreporter/process_reader/src/process_reader/windows.rs
+++ b/toolkit/crashreporter/process_reader/src/platform/windows.rs
@@ -15,7 +15,7 @@ use windows_sys::Win32::{
     System::{
         Diagnostics::Debug::ReadProcessMemory,
         ProcessStatus::{
-            GetModuleBaseNameW, K32EnumProcessModules, K32GetModuleInformation, MODULEINFO,
+            K32EnumProcessModules, K32GetModuleBaseNameW, K32GetModuleInformation, MODULEINFO,
         },
     },
 };
@@ -30,32 +30,54 @@ impl ProcessReader {
         Ok(ProcessReader { process })
     }
 
+    pub fn find_module(&self, module_name: &str) -> Result<usize, ProcessReaderError> {
+        let modules = self.get_module_list()?;
+
+        let module = modules.iter().find_map(|&module| {
+            let name = self.get_module_name(module);
+            // Crude way of mimicking Windows lower-case comparisons but
+            // sufficient for our use-cases.
+            if name.is_some_and(|name| name.eq_ignore_ascii_case(module_name)) {
+                self.get_module_info(module)
+                    .map(|module| module.lpBaseOfDll as usize)
+            } else {
+                None
+            }
+        });
+
+        module.ok_or(ProcessReaderError::ModuleNotFound)
+    }
+
     pub fn find_section(
         &self,
-        module_name: &str,
-        section_name: &str,
+        module_address: usize,
+        section_name: &[u8; 8],
     ) -> Result<usize, ProcessReaderError> {
-        let modules = self.get_module_list()?;
+        // We read only the first page from the module, this should be more than
+        // enough to read the header and section list. In the future we might do
+        // this incrementally but for now goblin requires an array to parse
+        // so we can't do it just yet.
+        const PAGE_SIZE: usize = 4096;
+        let bytes = self.copy_array(module_address as _, PAGE_SIZE)?;
+        let header = goblin::pe::header::Header::parse(&bytes)?;
 
-        modules
-            .iter()
-            .filter(|&&module| {
-                let name = self.get_module_name(module);
-                // Crude way of mimicking Windows lower-case comparisons but
-                // sufficient for our use-cases.
-                name.is_some_and(|name| name.eq_ignore_ascii_case(module_name))
-            })
-            .find_map(|&module| {
-                self.get_module_info(module).and_then(|info| {
-                    self.find_section_in_module(
-                        section_name,
-                        info.lpBaseOfDll as usize,
-                        info.SizeOfImage as usize,
-                    )
-                    .ok()
-                })
-            })
-            .ok_or(ProcessReaderError::InvalidAddress)
+        // Skip the PE header so we can parse the sections
+        let optional_header_offset = header.dos_header.pe_pointer as usize
+            + goblin::pe::header::SIZEOF_PE_MAGIC
+            + goblin::pe::header::SIZEOF_COFF_HEADER;
+        let offset =
+            &mut (optional_header_offset + header.coff_header.size_of_optional_header as usize);
+
+        let sections = header.coff_header.sections(&bytes, offset)?;
+
+        for section in sections {
+            if section.name.eq(section_name) {
+                let address = module_address.checked_add(section.virtual_address as usize);
+                return address.ok_or(ProcessReaderError::InvalidAddress);
+            }
+        }
+
+        Err(ProcessReaderError::SectionNotFound)
     }
 
     fn get_module_list(&self) -> Result<Vec<HMODULE>, ProcessReaderError> {
@@ -97,8 +119,9 @@ impl ProcessReader {
 
     fn get_module_name(&self, module: HMODULE) -> Option<String> {
         let mut path: [u16; MAX_PATH as usize] = [0; MAX_PATH as usize];
-        let res =
-            unsafe { GetModuleBaseNameW(self.process, module, (&mut path).as_mut_ptr(), MAX_PATH) };
+        let res = unsafe {
+            K32GetModuleBaseNameW(self.process, module, (&mut path).as_mut_ptr(), MAX_PATH)
+        };
 
         if res == 0 {
             None
@@ -128,46 +151,6 @@ impl ProcessReader {
         }
     }
 
-    fn find_section_in_module(
-        &self,
-        section_name: &str,
-        module_address: usize,
-        size: usize,
-    ) -> Result<usize, ProcessReaderError> {
-        // We read only the first page from the module, this should be more than
-        // enough to read the header and section list. In the future we might do
-        // this incrementally but for now goblin requires an array to parse
-        // so we can't do it just yet.
-        let page_size = 4096;
-        if size < page_size {
-            // Don't try to read from the target module if it's too small
-            return Err(ProcessReaderError::ReadFromProcessError(
-                ReadError::ReadProcessMemoryError,
-            ));
-        }
-
-        let bytes = self.copy_array(module_address as _, 4096)?;
-        let header = goblin::pe::header::Header::parse(&bytes)?;
-
-        // Skip the PE header so we can parse the sections
-        let optional_header_offset = header.dos_header.pe_pointer as usize
-            + goblin::pe::header::SIZEOF_PE_MAGIC
-            + goblin::pe::header::SIZEOF_COFF_HEADER;
-        let offset =
-            &mut (optional_header_offset + header.coff_header.size_of_optional_header as usize);
-
-        let sections = header.coff_header.sections(&bytes, offset)?;
-
-        for section in sections {
-            if section.name.eq(section_name.as_bytes()) {
-                let address = module_address.checked_add(section.virtual_address as usize);
-                return address.ok_or(ProcessReaderError::InvalidAddress);
-            }
-        }
-
-        Err(ProcessReaderError::SectionNotFound)
-    }
-
     pub fn copy_object_shallow<T>(&self, src: usize) -> Result<MaybeUninit<T>, ReadError> {
         let mut object = MaybeUninit::<T>::uninit();
         let res = unsafe {
diff --git a/toolkit/crashreporter/rust_minidump_writer_linux/src/lib.rs b/toolkit/crashreporter/rust_minidump_writer_linux/src/lib.rs
index fe5f30943e..21ae630c5e 100644
--- a/toolkit/crashreporter/rust_minidump_writer_linux/src/lib.rs
+++ b/toolkit/crashreporter/rust_minidump_writer_linux/src/lib.rs
@@ -3,7 +3,6 @@
  * You can obtain one at http://mozilla.org/MPL/2.0/. */
 extern crate minidump_writer;
 
-use anyhow;
 use libc::pid_t;
 use minidump_writer::crash_context::CrashContext;
 use minidump_writer::minidump_writer::MinidumpWriter;
diff --git a/toolkit/crashreporter/test/nsTestCrasher.cpp b/toolkit/crashreporter/test/nsTestCrasher.cpp
index 2148a60088..42b6a68b87 100644
--- a/toolkit/crashreporter/test/nsTestCrasher.cpp
+++ b/toolkit/crashreporter/test/nsTestCrasher.cpp
@@ -80,7 +80,7 @@ uint64_t x64CrashCFITest_EOF(uint64_t returnpfn, void*);
 #endif  // XP_WIN && HAVE_64BIT_BUILD && !defined(__MINGW32__)
 }
 
-// Keep these in sync with CrashTestUtils.jsm!
+// Keep these in sync with CrashTestUtils.sys.mjs!
 const int16_t CRASH_INVALID_POINTER_DEREF = 0;
 const int16_t CRASH_PURE_VIRTUAL_CALL = 1;
 const int16_t CRASH_OOM = 3;
diff --git a/toolkit/crashreporter/test/unit/head_win64cfi.js b/toolkit/crashreporter/test/unit/head_win64cfi.js
index 4df99213db..2daa64aecc 100644
--- a/toolkit/crashreporter/test/unit/head_win64cfi.js
+++ b/toolkit/crashreporter/test/unit/head_win64cfi.js
@@ -184,7 +184,7 @@ function assertStack(stack, expected) {
 
 // Performs a crash, runs minidump-analyzer, and checks expected stack analysis.
 //
-// how: The crash to perform. Constants defined in both CrashTestUtils.jsm
+// how: The crash to perform. Constants defined in both CrashTestUtils.sys.mjs
 //   and nsTestCrasher.cpp (i.e. CRASH_X64CFI_PUSH_NONVOL)
 // expectedStack: An array of {"symbol", "trust"} where trust is "cfi",
 //   "context", "scan", et al. May be null if you don't need to check the stack.
diff --git a/toolkit/crashreporter/test/unit/test_crash_stack_overflow.js b/toolkit/crashreporter/test/unit/test_crash_stack_overflow.js
index a47c217238..7c1d3821ec 100644
--- a/toolkit/crashreporter/test/unit/test_crash_stack_overflow.js
+++ b/toolkit/crashreporter/test/unit/test_crash_stack_overflow.js
@@ -12,7 +12,7 @@ add_task(async function run_test() {
       crashType = CrashTestUtils.CRASH_STACK_OVERFLOW;
       crashReporter.annotateCrashReport("TestKey", "TestValue");
     },
-    async function (mdump, extra, extraFile) {
+    async function (mdump, extra) {
       Assert.equal(extra.TestKey, "TestValue");
     },
     // process will exit with a zero exit status
diff --git a/toolkit/crashreporter/test/unit/test_crashreporter_appmem.js b/toolkit/crashreporter/test/unit/test_crashreporter_appmem.js
index f42fe10f0c..dcf5bd3153 100644
--- a/toolkit/crashreporter/test/unit/test_crashreporter_appmem.js
+++ b/toolkit/crashreporter/test/unit/test_crashreporter_appmem.js
@@ -4,7 +4,7 @@ add_task(async function run_test() {
       let appAddr = CrashTestUtils.saveAppMemory();
       crashReporter.registerAppMemory(appAddr, 32);
     },
-    function (mdump, extra) {
+    function (mdump) {
       Assert.ok(mdump.exists());
       Assert.ok(mdump.fileSize > 0);
       Assert.ok(CrashTestUtils.dumpCheckMemory(mdump.path));
diff --git a/toolkit/crashreporter/test/unit/test_event_files.js b/toolkit/crashreporter/test/unit/test_event_files.js
index 844d7700ff..f4054089ea 100644
--- a/toolkit/crashreporter/test/unit/test_event_files.js
+++ b/toolkit/crashreporter/test/unit/test_event_files.js
@@ -24,7 +24,7 @@ add_task(async function test_main_process_crash() {
         crashType = CrashTestUtils.CRASH_MOZ_CRASH;
         crashReporter.annotateCrashReport("ShutdownProgress", "event-test");
       },
-      (minidump, extra) => {
+      minidump => {
         basename = minidump.leafName;
         Object.defineProperty(cm, "_eventsDirs", { value: [getEventDir()] });
         cm.aggregateEventsFiles().then(resolve, reject);
diff --git a/toolkit/crashreporter/test/unit/test_override_exception_handler.js b/toolkit/crashreporter/test/unit/test_override_exception_handler.js
index 1b4dec8a61..caabc12de8 100644
--- a/toolkit/crashreporter/test/unit/test_override_exception_handler.js
+++ b/toolkit/crashreporter/test/unit/test_override_exception_handler.js
@@ -5,7 +5,7 @@ add_task(async function run_test() {
     function () {
       CrashTestUtils.TryOverrideExceptionHandler();
     },
-    function (mdump, extra) {},
+    function () {},
     true
   );
 });
diff --git a/toolkit/crashreporter/test/unit_ipc/test_content_memory_list.js b/toolkit/crashreporter/test/unit_ipc/test_content_memory_list.js
index 733d224160..b3770c7bcc 100644
--- a/toolkit/crashreporter/test/unit_ipc/test_content_memory_list.js
+++ b/toolkit/crashreporter/test/unit_ipc/test_content_memory_list.js
@@ -18,7 +18,7 @@ add_task(async function run_test() {
     is_win7_or_newer = true;
   }
 
-  await do_content_crash(null, function (mdump, extra) {
+  await do_content_crash(null, function (mdump) {
     Assert.ok(mdump.exists());
     Assert.ok(mdump.fileSize > 0);
     if (is_win7_or_newer) {
diff --git a/toolkit/crashreporter/tools/symbolstore.py b/toolkit/crashreporter/tools/symbolstore.py
index 8bc7a7120a..b7ad7752a8 100755
--- a/toolkit/crashreporter/tools/symbolstore.py
+++ b/toolkit/crashreporter/tools/symbolstore.py
@@ -23,6 +23,7 @@
 
 import ctypes
 import errno
+import io
 import os
 import platform
 import re
@@ -390,13 +391,13 @@ def validate_install_manifests(install_manifest_args):
 def make_file_mapping(install_manifests):
     file_mapping = {}
     for manifest, destination in install_manifests:
-        destination = os.path.abspath(destination)
+        absolute_destination = os.path.abspath(destination)
         reg = FileRegistry()
         manifest.populate_registry(reg)
         for dst, src in reg:
             if hasattr(src, "path"):
                 # Any paths that get compared to source file names need to go through realpath.
-                abs_dest = realpath(os.path.join(destination, dst))
+                abs_dest = realpath(os.path.join(absolute_destination, dst))
                 file_mapping[abs_dest] = realpath(src.path)
     return file_mapping
 
@@ -551,7 +552,58 @@ class Dumper:
         Get the commandline used to invoke dump_syms.
         """
         # The Mac dumper overrides this.
-        return [self.dump_syms, "--inlines", file]
+        cmdline = [
+            self.dump_syms,
+            "--inlines",
+        ]
+
+        cmdline.extend(self.dump_syms_extra_info())
+        cmdline.append(file)
+
+        return cmdline
+
+    def dump_syms_extra_info(self):
+        """
+        Returns an array with the additional parameters to add information
+        about the build to the dump_syms command-line
+        """
+        cmdline = [
+            "--extra-info",
+            "RELEASECHANNEL " + buildconfig.substs["MOZ_UPDATE_CHANNEL"],
+            "--extra-info",
+            "VERSION " + buildconfig.substs["MOZ_APP_VERSION"],
+        ]
+
+        if buildconfig.substs.get("MOZ_APP_VENDOR") is not None:
+            cmdline.extend(
+                [
+                    "--extra-info",
+                    "VENDOR " + buildconfig.substs["MOZ_APP_VENDOR"],
+                ]
+            )
+
+        if buildconfig.substs.get("MOZ_APP_BASENAME") is not None:
+            cmdline.extend(
+                [
+                    "--extra-info",
+                    "PRODUCTNAME " + buildconfig.substs["MOZ_APP_BASENAME"],
+                ]
+            )
+
+        # Add the build ID if it's present
+        path = os.path.join(buildconfig.topobjdir, "buildid.h")
+        try:
+            buildid = io.open(path, "r", encoding="utf-8").read().split()[2]
+            cmdline.extend(
+                [
+                    "--extra-info",
+                    "BUILDID " + buildid,
+                ]
+            )
+        except Exception:
+            pass
+
+        return cmdline
 
     def ProcessFileWork(
         self, file, arch_num, arch, vcs_root, dsymbundle=None, count_ctors=False
@@ -859,9 +911,8 @@ class Dumper_Linux(Dumper):
             full_path = os.path.normpath(os.path.join(self.symbol_path, rel_path))
             shutil.move(file_dbg, full_path)
             print(rel_path)
-        else:
-            if os.path.isfile(file_dbg):
-                os.unlink(file_dbg)
+        elif os.path.isfile(file_dbg):
+            os.unlink(file_dbg)
 
 
 class Dumper_Solaris(Dumper):
@@ -902,11 +953,22 @@ class Dumper_Mac(Dumper):
         # in order to dump all the symbols.
         if dsymbundle:
             # This is the .dSYM bundle.
-            return (
-                [self.dump_syms]
-                + arch.split()
-                + ["--inlines", "-j", "2", dsymbundle, file]
+            cmdline = [self.dump_syms]
+
+            cmdline.extend(arch.split())
+            cmdline.extend(
+                [
+                    "--inlines",
+                    "-j",
+                    "2",
+                ]
             )
+
+            cmdline.extend(self.dump_syms_extra_info())
+            cmdline.extend([dsymbundle, file])
+
+            return cmdline
+
         return Dumper.dump_syms_cmdline(self, file, arch)
 
     def GenerateDSYM(self, file):
@@ -1066,13 +1128,13 @@ to canonical locations in the source repository. Specify
 
     if len(args) < 3:
         parser.error("not enough arguments")
-        exit(1)
+        sys.exit(1)
 
     try:
         manifests = validate_install_manifests(options.install_manifests)
     except (IOError, ValueError) as e:
         parser.error(str(e))
-        exit(1)
+        sys.exit(1)
     file_mapping = make_file_mapping(manifests)
     _, bucket = get_s3_region_and_bucket()
     dumper = GetPlatformSpecificDumper(