Adding upstream version 110.0.1.upstream/110.0.1upstream

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

3 files changed, 2695 insertions, 0 deletions

diff --git a/toolkit/components/aboutmemory/content/aboutMemory.css b/toolkit/components/aboutmemory/content/aboutMemory.css
new file mode 100644
index 0000000000..dff9d42da0
--- /dev/null
+++ b/toolkit/components/aboutmemory/content/aboutMemory.css
@@ -0,0 +1,189 @@
+/* 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 version used for mobile is located at
+ * toolkit/themes/mobile/global/aboutMemory.css.
+ * Desktop-specific stuff is at the bottom of this file.
+ */
+
+html {
+  background: -moz-Dialog;
+  color: -moz-DialogText;
+  font: message-box;
+}
+
+body {
+  padding: 0 2em;
+  margin: 0;
+  min-width: 45em;
+  margin: auto;
+}
+
+/* The comment at the top of aboutMemory.xhtml explains this font choice. */
+pre {
+  font-family: DejaVu Sans Mono, Liberation Mono, Fira Mono, monospace;
+}
+
+div.ancillary {
+  margin: 0.5em 0;
+  user-select: none;
+}
+
+div.section {
+  padding: 2em;
+  margin: 1em 0em;
+  border: 1px solid ThreeDShadow;
+  border-radius: 10px;
+  background: Field;
+  color: FieldText;
+}
+
+div.outputContainer {
+  display: flex;
+}
+
+div.sections {
+  flex: 1;
+  min-width: 0;
+}
+
+div.sidebar {
+  flex: 0 0 max-content;
+  margin-left: 1em;
+}
+
+div.sidebarContents {
+  position: sticky;
+  top: 0.5em;
+}
+
+div.sidebarItem {
+  padding: 0.5em;
+  margin: 1em 0em;
+  border: 1px solid ThreeDShadow;
+  border-radius: 10px;
+  background: Field;
+  color: FieldText;
+  user-select: none;  /* no need to include this when cutting+pasting */
+}
+
+input.filterInput {
+  width: calc(100% - 1em);
+}
+
+ul.index {
+  list-style-position: inside;
+  margin: 0;
+  padding: 0;
+}
+
+ul.index > li {
+  padding-left: 0.5em;
+}
+
+div.opsRow {
+  padding: 0.5em;
+  margin-right: 0.5em;
+  margin-top: 0.5em;
+  border: 1px solid ThreeDShadow;
+  border-radius: 10px;
+  background: Field;
+  color: FieldText;
+  display: inline-block;
+}
+
+div.opsRowLabel, div.sidebarLabel {
+  display: block;
+  margin-bottom: 0.2em;
+  font-weight: bold;
+}
+
+.opsRowLabel label {
+  margin-left: 1em;
+  font-weight: normal;
+}
+
+div.non-verbose pre.entries {
+  overflow-x: hidden;
+  text-overflow: ellipsis;
+}
+
+h1 {
+  padding: 0;
+  margin: 0;
+  background: inherit; /* When sticky give it the solid background of the parent */
+  display: inline;  /* allow subsequent text to the right of the heading */
+  position: sticky; /* Stay at the top of the page when scrolling */
+  top: 0;
+  z-index: 1; /* When sticky it should appear above the tree lines */
+}
+
+h2 {
+  padding-left: .1em;
+}
+
+h3 {
+  display: inline;  /* allow subsequent text to the right of the heading */
+}
+
+a.upDownArrow {
+  font-size: 130%;
+  text-decoration: none;
+  user-select: none;  /* no need to include this when cutting+pasting */
+}
+
+.accuracyWarning, .badInputWarning, .invalid {
+  /*
+   * Technically this should be used with the default background colour,
+   * instead we're using the default field background colour,
+   * I hope this will be okay.
+   */
+  color: -moz-activehyperlinktext;
+}
+
+.treeline {
+  color: FieldText;
+  opacity: 0.5;
+}
+
+.mrValue {
+  font-weight: bold;
+}
+
+.hasKids {
+  cursor: pointer;
+}
+
+.hasKids:hover {
+  text-decoration: underline;
+}
+
+.noselect {
+  user-select: none;  /* no need to include this when cutting+pasting */
+}
+
+.option {
+  font-size: 80%;
+  user-select: none;  /* no need to include this when cutting+pasting */
+}
+
+.legend {
+  font-size: 80%;
+  user-select: none;  /* no need to include this when cutting+pasting */
+}
+
+.debug {
+  font-size: 80%;
+}
+
+.hidden {
+  display: none;
+}
+
+/* Desktop-specific parts go here. */
+
+.hasKids:hover {
+  text-decoration: underline;
+}
diff --git a/toolkit/components/aboutmemory/content/aboutMemory.js b/toolkit/components/aboutmemory/content/aboutMemory.js
new file mode 100644
index 0000000000..7cb5ccefb3
--- /dev/null
+++ b/toolkit/components/aboutmemory/content/aboutMemory.js
@@ -0,0 +1,2478 @@
+/* -*- indent-tabs-mode: nil; js-indent-level: 2 -*-*/
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+// You can direct about:memory to immediately load memory reports from a file
+// by providing a file= query string.  For example,
+//
+//     about:memory?file=/home/username/reports.json.gz
+//
+// "file=" is not case-sensitive.  We'll URI-unescape the contents of the
+// "file=" argument, and obviously the filename is case-sensitive iff you're on
+// a case-sensitive filesystem.  If you specify more than one "file=" argument,
+// only the first one is used.
+
+"use strict";
+
+// ---------------------------------------------------------------------------
+
+let CC = Components.Constructor;
+
+const KIND_NONHEAP = Ci.nsIMemoryReporter.KIND_NONHEAP;
+const KIND_HEAP = Ci.nsIMemoryReporter.KIND_HEAP;
+const KIND_OTHER = Ci.nsIMemoryReporter.KIND_OTHER;
+
+const UNITS_BYTES = Ci.nsIMemoryReporter.UNITS_BYTES;
+const UNITS_COUNT = Ci.nsIMemoryReporter.UNITS_COUNT;
+const UNITS_COUNT_CUMULATIVE = Ci.nsIMemoryReporter.UNITS_COUNT_CUMULATIVE;
+const UNITS_PERCENTAGE = Ci.nsIMemoryReporter.UNITS_PERCENTAGE;
+
+const { XPCOMUtils } = ChromeUtils.importESModule(
+  "resource://gre/modules/XPCOMUtils.sys.mjs"
+);
+const { NetUtil } = ChromeUtils.import("resource://gre/modules/NetUtil.jsm");
+ChromeUtils.defineESModuleGetters(this, {
+  Downloads: "resource://gre/modules/Downloads.sys.mjs",
+  FileUtils: "resource://gre/modules/FileUtils.sys.mjs",
+});
+
+XPCOMUtils.defineLazyGetter(this, "nsBinaryStream", () =>
+  CC(
+    "@mozilla.org/binaryinputstream;1",
+    "nsIBinaryInputStream",
+    "setInputStream"
+  )
+);
+XPCOMUtils.defineLazyGetter(this, "nsFile", () =>
+  CC("@mozilla.org/file/local;1", "nsIFile", "initWithPath")
+);
+XPCOMUtils.defineLazyGetter(this, "nsGzipConverter", () =>
+  CC(
+    "@mozilla.org/streamconv;1?from=gzip&to=uncompressed",
+    "nsIStreamConverter"
+  )
+);
+
+let gMgr = Cc["@mozilla.org/memory-reporter-manager;1"].getService(
+  Ci.nsIMemoryReporterManager
+);
+
+const gPageName = "about:memory";
+document.title = gPageName;
+
+const gMainProcessPrefix = "Main Process";
+
+const gFilterUpdateDelayMS = 300;
+
+let gIsDiff = false;
+
+let gCurrentReports = [];
+let gCurrentHasMozMallocUsableSize = false;
+let gCurrentIsDiff = false;
+
+let gFilter = "";
+
+// ---------------------------------------------------------------------------
+
+// Forward slashes in URLs in paths are represented with backslashes to avoid
+// being mistaken for path separators.  Paths/names where this hasn't been
+// undone are prefixed with "unsafe"; the rest are prefixed with "safe".
+function flipBackslashes(aUnsafeStr) {
+  // Save memory by only doing the replacement if it's necessary.
+  return !aUnsafeStr.includes("\\")
+    ? aUnsafeStr
+    : aUnsafeStr.replace(/\\/g, "/");
+}
+
+const gAssertionFailureMsgPrefix = "aboutMemory.js assertion failed: ";
+
+// This is used for things that should never fail, and indicate a defect in
+// this file if they do.
+function assert(aCond, aMsg) {
+  if (!aCond) {
+    reportAssertionFailure(aMsg);
+    throw new Error(gAssertionFailureMsgPrefix + aMsg);
+  }
+}
+
+// This is used for malformed input from memory reporters.
+function assertInput(aCond, aMsg) {
+  if (!aCond) {
+    throw new Error(`Invalid memory report(s): ${aMsg}`);
+  }
+}
+
+function handleException(aEx) {
+  let str = "" + aEx;
+  if (str.startsWith(gAssertionFailureMsgPrefix)) {
+    // Argh, assertion failure within this file!  Give up.
+    throw aEx;
+  } else {
+    // File or memory reporter problem.  Print a message.
+    updateMainAndFooter(str, NO_TIMESTAMP, HIDE_FOOTER, "badInputWarning");
+  }
+}
+
+function reportAssertionFailure(aMsg) {
+  let debug = Cc["@mozilla.org/xpcom/debug;1"].getService(Ci.nsIDebug2);
+  if (debug.isDebugBuild) {
+    debug.assertion(aMsg, "false", "aboutMemory.js", 0);
+  }
+}
+
+function debug(aVal) {
+  let section = appendElement(document.body, "div", "section");
+  appendElementWithText(section, "div", "debug", JSON.stringify(aVal));
+}
+
+function stringMatchesFilter(aString, aFilter) {
+  assert(
+    typeof aFilter == "string" || aFilter instanceof RegExp,
+    "unexpected aFilter type"
+  );
+
+  return typeof aFilter == "string"
+    ? aString.includes(aFilter)
+    : aFilter.test(aString);
+}
+
+// ---------------------------------------------------------------------------
+
+window.onunload = function() {};
+
+// ---------------------------------------------------------------------------
+
+// The <div> holding everything but the header and footer (if they're present).
+// It's what is updated each time the page changes.
+let gMain;
+
+// The <div> holding the footer.
+let gFooter;
+
+// The "verbose" checkbox.
+let gVerbose;
+
+// The "anonymize" checkbox.
+let gAnonymize;
+
+// Values for the |aFooterAction| argument to updateTitleMainAndFooter.
+const HIDE_FOOTER = 0;
+const SHOW_FOOTER = 1;
+
+// Values for the |aShowTimestamp| argument to updateTitleMainAndFooter.
+const NO_TIMESTAMP = 0;
+const SHOW_TIMESTAMP = 1;
+
+function updateTitleMainAndFooter(
+  aTitleNote,
+  aMsg,
+  aShowTimestamp,
+  aFooterAction,
+  aClassName
+) {
+  document.title = gPageName;
+  if (aTitleNote) {
+    document.title += ` (${aTitleNote})`;
+  }
+
+  // Clear gMain by replacing it with an empty node.
+  let tmp = gMain.cloneNode(false);
+  gMain.parentNode.replaceChild(tmp, gMain);
+  gMain = tmp;
+
+  gMain.classList.remove("hidden");
+  gMain.classList.remove("verbose");
+  gMain.classList.remove("non-verbose");
+  if (gVerbose) {
+    gMain.classList.add(gVerbose.checked ? "verbose" : "non-verbose");
+  }
+
+  let msgElement;
+  if (aMsg) {
+    let className = "section";
+    if (aClassName) {
+      className = className + " " + aClassName;
+    }
+    if (aShowTimestamp == SHOW_TIMESTAMP) {
+      // JS has many options for pretty-printing timestamps. We use
+      // toISOString() because it has sub-second granularity, which is useful
+      // if you quickly and repeatedly click one of the buttons.
+      aMsg += ` (${new Date().toISOString()})`;
+    }
+    msgElement = appendElementWithText(gMain, "div", className, aMsg);
+  }
+
+  switch (aFooterAction) {
+    case HIDE_FOOTER:
+      gFooter.classList.add("hidden");
+      break;
+    case SHOW_FOOTER:
+      gFooter.classList.remove("hidden");
+      break;
+    default:
+      assert(false, "bad footer action in updateTitleMainAndFooter");
+  }
+  return msgElement;
+}
+
+function updateMainAndFooter(aMsg, aShowTimestamp, aFooterAction, aClassName) {
+  return updateTitleMainAndFooter(
+    "",
+    aMsg,
+    aShowTimestamp,
+    aFooterAction,
+    aClassName
+  );
+}
+
+function appendTextNode(aP, aText) {
+  let e = document.createTextNode(aText);
+  aP.appendChild(e);
+  return e;
+}
+
+function appendElement(aP, aTagName, aClassName) {
+  let e = newElement(aTagName, aClassName);
+  aP.appendChild(e);
+  return e;
+}
+
+function appendElementWithText(aP, aTagName, aClassName, aText) {
+  let e = appendElement(aP, aTagName, aClassName);
+  // Setting textContent clobbers existing children, but there are none.  More
+  // importantly, it avoids creating a JS-land object for the node, saving
+  // memory.
+  e.textContent = aText;
+  return e;
+}
+
+function newElement(aTagName, aClassName) {
+  let e = document.createElement(aTagName);
+  if (aClassName) {
+    e.className = aClassName;
+  }
+  return e;
+}
+
+// ---------------------------------------------------------------------------
+
+const explicitTreeDescription =
+  "This tree covers explicit memory allocations by the application.  It includes \
+\n\n\
+* all allocations made at the heap allocation level (via functions such as malloc, \
+calloc, realloc, memalign, operator new, and operator new[]) that have not been \
+explicitly decommitted (i.e. evicted from memory and swap), and \
+\n\n\
+* some allocations (those covered by memory reporters) made at the operating \
+system level (via calls to functions such as VirtualAlloc, vm_allocate, and \
+mmap), \
+\n\n\
+* where possible, the overhead of the heap allocator itself.\
+\n\n\
+It excludes memory that is mapped implicitly such as code and data segments, \
+and thread stacks. \
+\n\n\
+'explicit' is not guaranteed to cover every explicit allocation, but it does cover \
+most (including the entire heap), and therefore it is the single best number to \
+focus on when trying to reduce memory usage.";
+
+// ---------------------------------------------------------------------------
+
+function appendButton(aP, aTitle, aOnClick, aText, aId) {
+  let b = appendElementWithText(aP, "button", "", aText);
+  b.title = aTitle;
+  b.onclick = aOnClick;
+  if (aId) {
+    b.id = aId;
+  }
+  return b;
+}
+
+function appendHiddenFileInput(aP, aId, aChangeListener) {
+  let input = appendElementWithText(aP, "input", "hidden", "");
+  input.type = "file";
+  input.id = aId; // used in testing
+  input.addEventListener("change", aChangeListener);
+  return input;
+}
+
+window.onload = function() {
+  // Generate the header.
+
+  let header = appendElement(document.body, "div", "ancillary");
+
+  // A hidden file input element that can be invoked when necessary.
+  let fileInput1 = appendHiddenFileInput(header, "fileInput1", function() {
+    let file = this.files[0];
+    let filename = file.mozFullPath;
+    updateAboutMemoryFromFile(filename);
+  });
+
+  // Ditto.
+  let fileInput2 = appendHiddenFileInput(header, "fileInput2", function(aElem) {
+    let file = this.files[0];
+    // First time around, we stash a copy of the filename and reinvoke.  Second
+    // time around we do the diff and display.
+    if (!this.filename1) {
+      this.filename1 = file.mozFullPath;
+
+      // aElem.skipClick is only true when testing -- it allows fileInput2's
+      // onchange handler to be re-called without having to go via the file
+      // picker.
+      if (!aElem.skipClick) {
+        this.click();
+      }
+    } else {
+      let filename1 = this.filename1;
+      delete this.filename1;
+      updateAboutMemoryFromTwoFiles(filename1, file.mozFullPath);
+    }
+  });
+
+  const CuDesc = "Measure current memory reports and show.";
+  const LdDesc = "Load memory reports from file and show.";
+  const DfDesc =
+    "Load memory report data from two files and show the difference.";
+
+  const SvDesc = "Save memory reports to file.";
+
+  const GCDesc = "Do a global garbage collection.";
+  const CCDesc = "Do a cycle collection.";
+  const MMDesc =
+    'Send three "heap-minimize" notifications in a ' +
+    "row.  Each notification triggers a global garbage " +
+    "collection followed by a cycle collection, and causes the " +
+    "process to reduce memory usage in other ways, e.g. by " +
+    "flushing various caches.";
+
+  const GCAndCCLogDesc =
+    "Save garbage collection log and concise cycle " +
+    "collection log.\n" +
+    "WARNING: These logs may be large (>1GB).";
+  const GCAndCCAllLogDesc =
+    "Save garbage collection log and verbose cycle " +
+    "collection log.\n" +
+    "WARNING: These logs may be large (>1GB).";
+
+  const DMDEnabledDesc =
+    "Analyze memory reports coverage and save the " +
+    "output to the temp directory.\n";
+  const DMDDisabledDesc =
+    "DMD is not running. Please re-start with $DMD and " +
+    "the other relevant environment variables set " +
+    "appropriately.";
+
+  let ops = appendElement(header, "div", "");
+
+  let row1 = appendElement(ops, "div", "opsRow");
+
+  let labelDiv1 = appendElementWithText(
+    row1,
+    "div",
+    "opsRowLabel",
+    "Show memory reports"
+  );
+  labelDiv1.setAttribute("role", "heading");
+  labelDiv1.setAttribute("aria-level", "1");
+  let label1 = appendElementWithText(labelDiv1, "label", "");
+  gVerbose = appendElement(label1, "input", "");
+  gVerbose.type = "checkbox";
+  gVerbose.id = "verbose"; // used for testing
+  appendTextNode(label1, "verbose");
+
+  // The "measureButton" id is used for testing.
+  appendButton(row1, CuDesc, doMeasure, "Measure", "measureButton");
+  appendButton(row1, LdDesc, () => fileInput1.click(), "Load…");
+  appendButton(row1, DfDesc, () => fileInput2.click(), "Load and diff…");
+
+  let row2 = appendElement(ops, "div", "opsRow");
+
+  let labelDiv2 = appendElementWithText(
+    row2,
+    "div",
+    "opsRowLabel",
+    "Save memory reports"
+  );
+  labelDiv2.setAttribute("role", "heading");
+  labelDiv2.setAttribute("aria-level", "1");
+  appendButton(row2, SvDesc, saveReportsToFile, "Measure and save…");
+
+  // XXX: this isn't a great place for this checkbox, but I can't think of
+  // anywhere better.
+  let label2 = appendElementWithText(labelDiv2, "label", "");
+  gAnonymize = appendElement(label2, "input", "");
+  gAnonymize.type = "checkbox";
+  appendTextNode(label2, "anonymize");
+
+  let row3 = appendElement(ops, "div", "opsRow");
+
+  let labelDiv3 = appendElementWithText(
+    row3,
+    "div",
+    "opsRowLabel",
+    "Free memory"
+  );
+  labelDiv3.setAttribute("role", "heading");
+  labelDiv3.setAttribute("aria-level", "1");
+  appendButton(row3, GCDesc, doGC, "GC");
+  appendButton(row3, CCDesc, doCC, "CC");
+  appendButton(row3, MMDesc, doMMU, "Minimize memory usage");
+
+  let row4 = appendElement(ops, "div", "opsRow");
+
+  let labelDiv4 = appendElementWithText(
+    row4,
+    "div",
+    "opsRowLabel",
+    "Save GC & CC logs"
+  );
+  labelDiv4.setAttribute("role", "heading");
+  labelDiv4.setAttribute("aria-level", "1");
+  appendButton(
+    row4,
+    GCAndCCLogDesc,
+    saveGCLogAndConciseCCLog,
+    "Save concise",
+    "saveLogsConcise"
+  );
+  appendButton(
+    row4,
+    GCAndCCAllLogDesc,
+    saveGCLogAndVerboseCCLog,
+    "Save verbose",
+    "saveLogsVerbose"
+  );
+
+  // Three cases here:
+  // - DMD is disabled (i.e. not built): don't show the button.
+  // - DMD is enabled but is not running: show the button, but disable it.
+  // - DMD is enabled and is running: show the button and enable it.
+  if (gMgr.isDMDEnabled) {
+    let row5 = appendElement(ops, "div", "opsRow");
+
+    let labelDiv5 = appendElementWithText(
+      row5,
+      "div",
+      "opsRowLabel",
+      "Save DMD output"
+    );
+    labelDiv5.setAttribute("role", "heading");
+    labelDiv5.setAttribute("aria-level", "1");
+    let enableButtons = gMgr.isDMDRunning;
+
+    let dmdButton = appendButton(
+      row5,
+      enableButtons ? DMDEnabledDesc : DMDDisabledDesc,
+      doDMD,
+      "Save"
+    );
+    dmdButton.disabled = !enableButtons;
+  }
+
+  // Generate the main div, where content ("section" divs) will go.  It's
+  // hidden at first.
+
+  gMain = appendElement(document.body, "div", "");
+  gMain.id = "mainDiv";
+
+  // Generate the footer.  It's hidden at first.
+
+  gFooter = appendElement(document.body, "div", "ancillary hidden");
+  gFooter.setAttribute("role", "contentinfo");
+
+  if (Services.policies.isAllowed("aboutSupport")) {
+    let a = appendElementWithText(
+      gFooter,
+      "a",
+      "option",
+      "Troubleshooting information"
+    );
+    a.href = "about:support";
+  }
+
+  let legendText1 =
+    "Click on a non-leaf node in a tree to expand ('++') " +
+    "or collapse ('--') its children.";
+  let legendText2 =
+    "Hover the pointer over the name of a memory report " +
+    "to see a description of what it measures.";
+
+  appendElementWithText(gFooter, "div", "legend", legendText1);
+  appendElementWithText(gFooter, "div", "legend hiddenOnMobile", legendText2);
+
+  // See if we're loading from a file.  (Because about:memory is a non-standard
+  // URL, location.search is undefined, so we have to use location.href
+  // instead.)
+  let search = location.href.split("?")[1];
+  if (search) {
+    let searchSplit = search.split("&");
+    for (let s of searchSplit) {
+      if (s.toLowerCase().startsWith("file=")) {
+        let filename = s.substring("file=".length);
+        updateAboutMemoryFromFile(decodeURIComponent(filename));
+        return;
+      }
+    }
+  }
+};
+
+// ---------------------------------------------------------------------------
+
+function doGC() {
+  Services.obs.notifyObservers(null, "child-gc-request");
+  Cu.forceGC();
+  updateMainAndFooter(
+    "Garbage collection completed",
+    SHOW_TIMESTAMP,
+    HIDE_FOOTER
+  );
+}
+
+function doCC() {
+  Services.obs.notifyObservers(null, "child-cc-request");
+  window.windowUtils.cycleCollect();
+  updateMainAndFooter(
+    "Cycle collection completed",
+    SHOW_TIMESTAMP,
+    HIDE_FOOTER
+  );
+}
+
+function doMMU() {
+  Services.obs.notifyObservers(null, "child-mmu-request");
+  gMgr.minimizeMemoryUsage(() =>
+    updateMainAndFooter(
+      "Memory minimization completed",
+      SHOW_TIMESTAMP,
+      HIDE_FOOTER
+    )
+  );
+}
+
+function doMeasure() {
+  updateAboutMemoryFromReporters();
+}
+
+function saveGCLogAndConciseCCLog() {
+  dumpGCLogAndCCLog(false);
+}
+
+function saveGCLogAndVerboseCCLog() {
+  dumpGCLogAndCCLog(true);
+}
+
+function doDMD() {
+  updateMainAndFooter(
+    "Saving memory reports and DMD output...",
+    NO_TIMESTAMP,
+    HIDE_FOOTER
+  );
+  try {
+    let dumper = Cc["@mozilla.org/memory-info-dumper;1"].getService(
+      Ci.nsIMemoryInfoDumper
+    );
+
+    dumper.dumpMemoryInfoToTempDir(
+      /* identifier = */ "",
+      gAnonymize.checked,
+      /* minimize = */ false
+    );
+    updateMainAndFooter(
+      "Saved memory reports and DMD reports analysis " +
+        "to the temp directory",
+      SHOW_TIMESTAMP,
+      HIDE_FOOTER
+    );
+  } catch (ex) {
+    updateMainAndFooter(ex.toString(), NO_TIMESTAMP, HIDE_FOOTER);
+  }
+}
+
+function dumpGCLogAndCCLog(aVerbose) {
+  let dumper = Cc["@mozilla.org/memory-info-dumper;1"].getService(
+    Ci.nsIMemoryInfoDumper
+  );
+
+  let inProgress = updateMainAndFooter(
+    "Saving logs...",
+    NO_TIMESTAMP,
+    HIDE_FOOTER
+  );
+  let section = appendElement(gMain, "div", "section");
+
+  function displayInfo(aGCLog, aCCLog, aIsParent) {
+    appendElementWithText(section, "div", "", "Saved GC log to " + aGCLog.path);
+
+    let ccLogType = aVerbose ? "verbose" : "concise";
+    appendElementWithText(
+      section,
+      "div",
+      "",
+      "Saved " + ccLogType + " CC log to " + aCCLog.path
+    );
+  }
+
+  dumper.dumpGCAndCCLogsToFile("", aVerbose, /* dumpChildProcesses = */ true, {
+    onDump: displayInfo,
+    onFinish() {
+      inProgress.remove();
+    },
+  });
+}
+
+/**
+ * Top-level function that does the work of generating the page from the memory
+ * reporters.
+ */
+function updateAboutMemoryFromReporters() {
+  updateMainAndFooter("Measuring...", NO_TIMESTAMP, HIDE_FOOTER);
+
+  try {
+    gCurrentReports = [];
+    gCurrentHasMozMallocUsableSize = gMgr.hasMozMallocUsableSize;
+    gCurrentIsDiff = false;
+    gFilter = "";
+
+    // Record the reports from the live memory reporters then process them.
+    let handleReport = function(
+      aProcess,
+      aUnsafePath,
+      aKind,
+      aUnits,
+      aAmount,
+      aDescription
+    ) {
+      gCurrentReports.push({
+        process: aProcess,
+        path: aUnsafePath,
+        kind: aKind,
+        units: aUnits,
+        amount: aAmount,
+        description: aDescription,
+      });
+    };
+
+    let displayReports = function() {
+      updateTitleMainAndFooter(
+        "live measurement",
+        "",
+        NO_TIMESTAMP,
+        SHOW_FOOTER
+      );
+      updateAboutMemoryFromCurrentData();
+    };
+
+    gMgr.getReports(
+      handleReport,
+      null,
+      displayReports,
+      null,
+      gAnonymize.checked
+    );
+  } catch (ex) {
+    handleException(ex);
+  }
+}
+
+// Increment this if the JSON format changes.
+//
+let gCurrentFileFormatVersion = 1;
+
+/**
+ * Parse a string as JSON and extract the |memory_report| property if it has
+ * one, which indicates the string is from a crash dump.
+ *
+ * @param aStr
+ *        The string.
+ * @return The extracted object.
+ */
+function parseAndUnwrapIfCrashDump(aStr) {
+  let obj = JSON.parse(aStr);
+  if (obj.memory_report !== undefined) {
+    // It looks like a crash dump. The memory reports should be in the
+    // |memory_report| property.
+    obj = obj.memory_report;
+  }
+  return obj;
+}
+
+/**
+ * Populate about:memory using the data stored in gCurrentReports and
+ * gCurrentHasMozMallocUsableSize.
+ */
+function updateAboutMemoryFromCurrentData() {
+  function processCurrentMemoryReports(aHandleReport, aDisplayReports) {
+    for (let r of gCurrentReports) {
+      aHandleReport(
+        r.process,
+        r.path,
+        r.kind,
+        r.units,
+        r.amount,
+        r.description,
+        r._presence
+      );
+    }
+    aDisplayReports();
+  }
+
+  gIsDiff = gCurrentIsDiff;
+  appendAboutMemoryMain(
+    processCurrentMemoryReports,
+    gFilter,
+    gCurrentHasMozMallocUsableSize
+  );
+  gIsDiff = false;
+}
+
+/**
+ * Populate about:memory using the data in the given JSON object.
+ *
+ * @param aObj
+ *        An object that (hopefully!) conforms to the JSON schema used by
+ *        nsIMemoryInfoDumper.
+ */
+function updateAboutMemoryFromJSONObject(aObj) {
+  try {
+    assertInput(
+      aObj.version === gCurrentFileFormatVersion,
+      "data version number missing or doesn't match"
+    );
+    assertInput(
+      aObj.hasMozMallocUsableSize !== undefined,
+      "missing 'hasMozMallocUsableSize' property"
+    );
+    assertInput(
+      aObj.reports && aObj.reports instanceof Array,
+      "missing or non-array 'reports' property"
+    );
+
+    gCurrentReports = aObj.reports.concat();
+    gCurrentHasMozMallocUsableSize = aObj.hasMozMallocUsableSize;
+    gCurrentIsDiff = gIsDiff;
+    gFilter = "";
+
+    updateAboutMemoryFromCurrentData();
+  } catch (ex) {
+    handleException(ex);
+  }
+}
+
+/**
+ * Populate about:memory using the data in the given JSON string.
+ *
+ * @param aStr
+ *        A string containing JSON data conforming to the schema used by
+ *        nsIMemoryReporterManager::dumpReports.
+ */
+function updateAboutMemoryFromJSONString(aStr) {
+  try {
+    let obj = parseAndUnwrapIfCrashDump(aStr);
+    updateAboutMemoryFromJSONObject(obj);
+  } catch (ex) {
+    handleException(ex);
+  }
+}
+
+/**
+ * Loads the contents of a file into a string and passes that to a callback.
+ *
+ * @param aFilename
+ *        The name of the file being read from.
+ * @param aTitleNote
+ *        A description to put in the page title upon completion.
+ * @param aFn
+ *        The function to call and pass the read string to upon completion.
+ */
+function loadMemoryReportsFromFile(aFilename, aTitleNote, aFn) {
+  updateMainAndFooter("Loading...", NO_TIMESTAMP, HIDE_FOOTER);
+
+  try {
+    let reader = new FileReader();
+    reader.onerror = () => {
+      throw new Error("FileReader.onerror");
+    };
+    reader.onabort = () => {
+      throw new Error("FileReader.onabort");
+    };
+    reader.onload = aEvent => {
+      // Clear "Loading..." from above.
+      updateTitleMainAndFooter(aTitleNote, "", NO_TIMESTAMP, SHOW_FOOTER);
+      aFn(aEvent.target.result);
+    };
+
+    // If it doesn't have a .gz suffix, read it as a (legacy) ungzipped file.
+    if (!aFilename.endsWith(".gz")) {
+      File.createFromFileName(aFilename).then(file => {
+        reader.readAsText(file);
+      });
+      return;
+    }
+
+    // Read compressed gzip file.
+    let converter = new nsGzipConverter();
+    converter.asyncConvertData(
+      "gzip",
+      "uncompressed",
+      {
+        data: [],
+        onStartRequest(aR, aC) {},
+        onDataAvailable(aR, aStream, aO, aCount) {
+          let bi = new nsBinaryStream(aStream);
+          this.data.push(bi.readBytes(aCount));
+        },
+        onStopRequest(aR, aC, aStatusCode) {
+          try {
+            if (!Components.isSuccessCode(aStatusCode)) {
+              throw new Components.Exception(
+                "Error while reading gzip file",
+                aStatusCode
+              );
+            }
+            reader.readAsText(new Blob(this.data));
+          } catch (ex) {
+            handleException(ex);
+          }
+        },
+      },
+      null
+    );
+
+    let file = new nsFile(aFilename);
+    let fileChan = NetUtil.newChannel({
+      uri: Services.io.newFileURI(file),
+      loadUsingSystemPrincipal: true,
+    });
+    fileChan.asyncOpen(converter);
+  } catch (ex) {
+    handleException(ex);
+  }
+}
+
+/**
+ * Like updateAboutMemoryFromReporters(), but gets its data from a file instead
+ * of the memory reporters.
+ *
+ * @param aFilename
+ *        The name of the file being read from.  The expected format of the
+ *        file's contents is described in a comment in nsIMemoryInfoDumper.idl.
+ */
+function updateAboutMemoryFromFile(aFilename) {
+  loadMemoryReportsFromFile(
+    aFilename,
+    /* title note */ aFilename,
+    updateAboutMemoryFromJSONString
+  );
+}
+
+/**
+ * Like updateAboutMemoryFromFile(), but gets its data from a two files and
+ * diffs them.
+ *
+ * @param aFilename1
+ *        The name of the first file being read from.
+ * @param aFilename2
+ *        The name of the first file being read from.
+ */
+function updateAboutMemoryFromTwoFiles(aFilename1, aFilename2) {
+  let titleNote = `diff of ${aFilename1} and ${aFilename2}`;
+  loadMemoryReportsFromFile(aFilename1, titleNote, function(aStr1) {
+    loadMemoryReportsFromFile(aFilename2, titleNote, function(aStr2) {
+      try {
+        let obj1 = parseAndUnwrapIfCrashDump(aStr1);
+        let obj2 = parseAndUnwrapIfCrashDump(aStr2);
+        gIsDiff = true;
+        updateAboutMemoryFromJSONObject(diffJSONObjects(obj1, obj2));
+        gIsDiff = false;
+      } catch (ex) {
+        handleException(ex);
+      }
+    });
+  });
+}
+
+// ---------------------------------------------------------------------------
+
+// Something unlikely to appear in a process name.
+let kProcessPathSep = "^:^:^";
+
+// Short for "diff report".
+function DReport(aKind, aUnits, aAmount, aDescription, aNMerged, aPresence) {
+  this._kind = aKind;
+  this._units = aUnits;
+  this._amount = aAmount;
+  this._description = aDescription;
+  this._nMerged = aNMerged;
+  if (aPresence !== undefined) {
+    this._presence = aPresence;
+  }
+}
+
+DReport.prototype = {
+  assertCompatible(aKind, aUnits) {
+    assert(this._kind == aKind, "Mismatched kinds");
+    assert(this._units == aUnits, "Mismatched units");
+
+    // We don't check that the "description" properties match.  This is because
+    // on Linux we can get cases where the paths are the same but the
+    // descriptions differ, like this:
+    //
+    //   "path": "size/other-files/icon-theme.cache/[r--p]",
+    //   "description": "/usr/share/icons/gnome/icon-theme.cache (read-only, not executable, private)"
+    //
+    //   "path": "size/other-files/icon-theme.cache/[r--p]"
+    //   "description": "/usr/share/icons/hicolor/icon-theme.cache (read-only, not executable, private)"
+    //
+    // In those cases, we just use the description from the first-encountered
+    // one, which is what about:memory also does.
+    // (Note: reports with those paths are no longer generated, but allowing
+    // the descriptions to differ seems reasonable.)
+  },
+
+  merge(aJr) {
+    this.assertCompatible(aJr.kind, aJr.units);
+    this._amount += aJr.amount;
+    this._nMerged++;
+  },
+
+  toJSON(aProcess, aPath, aAmount) {
+    return {
+      process: aProcess,
+      path: aPath,
+      kind: this._kind,
+      units: this._units,
+      amount: aAmount,
+      description: this._description,
+      _presence: this._presence,
+    };
+  },
+};
+
+// Constants that indicate if a DReport was present only in one of the data
+// sets, or had to be added for balance.
+DReport.PRESENT_IN_FIRST_ONLY = 1;
+DReport.PRESENT_IN_SECOND_ONLY = 2;
+DReport.ADDED_FOR_BALANCE = 3;
+
+/**
+ * Return true if the report contains a webIsolated process,
+ * which is a good indication that Fission is enabled.
+ */
+function hasWebIsolatedProcess(aJSONReports) {
+  for (let jr of aJSONReports) {
+    assert(jr.process !== undefined, "Missing process");
+    if (jr.process.startsWith("webIsolated")) {
+      return true;
+    }
+  }
+  return false;
+}
+
+/**
+ * Make a report map, which has combined path+process strings for keys, and
+ * DReport objects for values.
+ *
+ * @param aJSONReports
+ *        The |reports| field of a JSON object.
+ * @param aForgetIsolation
+          If this is true, treat webIsolated processes like web processes.
+ * @return The constructed report map.
+ */
+function makeDReportMap(aJSONReports, aForgetIsolation) {
+  let dreportMap = {};
+  for (let jr of aJSONReports) {
+    assert(jr.process !== undefined, "Missing process");
+    assert(jr.path !== undefined, "Missing path");
+    assert(jr.kind !== undefined, "Missing kind");
+    assert(jr.units !== undefined, "Missing units");
+    assert(jr.amount !== undefined, "Missing amount");
+    assert(jr.description !== undefined, "Missing description");
+
+    // Strip out some non-deterministic stuff that prevents clean diffs.
+    // Ideally the memory reports themselves would contain information about
+    // which parts of the the process and path need to be stripped -- saving us
+    // from hardwiring knowledge of specific reporters here -- but we have no
+    // mechanism for that. (Any future redesign of how memory reporters work
+    // should include such a mechanism.)
+
+    // Strip PIDs:
+    // - pid 123
+    // - pid=123
+    let pidRegex = /pid([ =])\d+/g;
+    let pidSubst = "pid$1NNN";
+    let process = jr.process.replace(pidRegex, pidSubst);
+    let path = jr.path.replace(pidRegex, pidSubst);
+
+    if (aForgetIsolation && process.startsWith("webIsolated")) {
+      process = "web (pid NNN)";
+    }
+
+    // Strip TIDs and threadpool IDs.
+    path = path.replace(/\(tid=(\d+)\)/, "(tid=NNN)");
+    path = path.replace(/#\d+ \(tid=NNN\)/, "#N (tid=NNN)");
+
+    // Strip addresses:
+    // - .../js-zone(0x12345678)/...
+    // - .../zone(0x12345678)/...
+    // - .../worker(<URL>, 0x12345678)/...
+    path = path.replace(/zone\(0x[0-9A-Fa-f]+\)\//, "zone(0xNNN)/");
+    path = path.replace(
+      /\/worker\((.+), 0x[0-9A-Fa-f]+\)\//,
+      "/worker($1, 0xNNN)/"
+    );
+
+    // Strip top window IDs:
+    // - explicit/window-objects/top(<URL>, id=123)/...
+    // - event-counts/window-objects/top(<URL>, id=123)/...
+    path = path.replace(
+      /^((?:explicit|event-counts)\/window-objects\/top\(.*, id=)\d+\)/,
+      "$1NNN)"
+    );
+
+    // Strip null principal UUIDs (but not other UUIDs, because they may be
+    // deterministic, such as those used by add-ons).
+    path = path.replace(
+      /moz-nullprincipal:{........-....-....-....-............}/g,
+      "moz-nullprincipal:{NNNNNNNN-NNNN-NNNN-NNNN-NNNNNNNNNNNN}"
+    );
+
+    // Strip segment counts from address-space.
+    if (path.startsWith("address-space")) {
+      path = path.replace(/\(segments=\d+\)/g, "(segments=NNNN)");
+    }
+
+    // Normalize omni.ja! paths.
+    path = path.replace(
+      /jar:file:\\\\\\(.+)\\omni.ja!/,
+      "jar:file:\\\\\\...\\omni.ja!"
+    );
+
+    // Normalize script source counts.
+    path = path.replace(/source\(scripts=(\d+), /, "source(scripts=NNN, ");
+
+    let processPath = process + kProcessPathSep + path;
+    let rOld = dreportMap[processPath];
+    if (rOld === undefined) {
+      dreportMap[processPath] = new DReport(
+        jr.kind,
+        jr.units,
+        jr.amount,
+        jr.description,
+        1,
+        undefined
+      );
+    } else {
+      rOld.merge(jr);
+    }
+  }
+  return dreportMap;
+}
+
+// Return a new dreportMap which is the diff of two dreportMaps.  Empties
+// aDReportMap2 along the way.
+function diffDReportMaps(aDReportMap1, aDReportMap2) {
+  let result = {};
+
+  for (let processPath in aDReportMap1) {
+    let r1 = aDReportMap1[processPath];
+    let r2 = aDReportMap2[processPath];
+    let r2_amount, r2_nMerged;
+    let presence;
+    if (r2 !== undefined) {
+      r1.assertCompatible(r2._kind, r2._units);
+      r2_amount = r2._amount;
+      r2_nMerged = r2._nMerged;
+      delete aDReportMap2[processPath];
+      presence = undefined; // represents that it's present in both
+    } else {
+      r2_amount = 0;
+      r2_nMerged = 0;
+      presence = DReport.PRESENT_IN_FIRST_ONLY;
+    }
+    result[processPath] = new DReport(
+      r1._kind,
+      r1._units,
+      r2_amount - r1._amount,
+      r1._description,
+      Math.max(r1._nMerged, r2_nMerged),
+      presence
+    );
+  }
+
+  for (let processPath in aDReportMap2) {
+    let r2 = aDReportMap2[processPath];
+    result[processPath] = new DReport(
+      r2._kind,
+      r2._units,
+      r2._amount,
+      r2._description,
+      r2._nMerged,
+      DReport.PRESENT_IN_SECOND_ONLY
+    );
+  }
+
+  return result;
+}
+
+function makeJSONReports(aDReportMap) {
+  let reports = [];
+  for (let processPath in aDReportMap) {
+    let r = aDReportMap[processPath];
+    if (r._amount !== 0) {
+      // If _nMerged > 1, we give the full (aggregated) amount in the first
+      // copy, and then use amount=0 in the remainder.  When viewed in
+      // about:memory, this shows up as an entry with a "[2]"-style suffix
+      // and the correct amount.
+      let split = processPath.split(kProcessPathSep);
+      assert(split.length >= 2);
+      let process = split.shift();
+      let path = split.join();
+      reports.push(r.toJSON(process, path, r._amount));
+      for (let i = 1; i < r._nMerged; i++) {
+        reports.push(r.toJSON(process, path, 0));
+      }
+    }
+  }
+
+  return reports;
+}
+
+// Diff two JSON objects holding memory reports.
+function diffJSONObjects(aJson1, aJson2) {
+  function simpleProp(aProp) {
+    assert(
+      aJson1[aProp] !== undefined && aJson1[aProp] === aJson2[aProp],
+      aProp + " properties don't match"
+    );
+    return aJson1[aProp];
+  }
+
+  // If one report we're diffing contains webIsolated processes, but the other
+  // does not, then we're probably comparing a report with Fission enabled with
+  // one where it is not enabled. In this case, we want to make all of the
+  // webIsolated processes look like plain old web processes to get a better
+  // diff.
+  let hasIsolated1 = hasWebIsolatedProcess(aJson1.reports);
+  let hasIsolated2 = hasWebIsolatedProcess(aJson2.reports);
+  let eitherIsolated = hasIsolated1 || hasIsolated2;
+  let forgetIsolation = hasIsolated1 != hasIsolated2 && eitherIsolated;
+
+  return {
+    version: simpleProp("version"),
+
+    hasMozMallocUsableSize: simpleProp("hasMozMallocUsableSize"),
+
+    reports: makeJSONReports(
+      diffDReportMaps(
+        makeDReportMap(aJson1.reports, forgetIsolation),
+        makeDReportMap(aJson2.reports, forgetIsolation)
+      )
+    ),
+  };
+}
+
+// ---------------------------------------------------------------------------
+
+// |PColl| is short for "process collection".
+function PColl() {
+  this._trees = {};
+  this._degenerates = {};
+  this._heapTotal = 0;
+}
+
+/**
+ * Processes reports (whether from reporters or from a file) and append the
+ * main part of the page.
+ *
+ * @param aProcessReports
+ *        Function that extracts the memory reports from the reporters or from
+ *        file.
+ * @param aFilter
+ *        String or RegExp used to filter reports by their path.
+ * @param aHasMozMallocUsableSize
+ *        Boolean indicating if moz_malloc_usable_size works.
+ */
+function appendAboutMemoryMain(
+  aProcessReports,
+  aFilter,
+  aHasMozMallocUsableSize
+) {
+  let pcollsByProcess = {};
+  let infoByProcess = {};
+
+  function handleReport(
+    aProcess,
+    aUnsafePath,
+    aKind,
+    aUnits,
+    aAmount,
+    aDescription,
+    aPresence
+  ) {
+    if (aUnsafePath.startsWith("explicit/")) {
+      assertInput(
+        aKind === KIND_HEAP || aKind === KIND_NONHEAP,
+        "bad explicit kind"
+      );
+      assertInput(aUnits === UNITS_BYTES, "bad explicit units");
+    }
+
+    assert(
+      aPresence === undefined ||
+        aPresence == DReport.PRESENT_IN_FIRST_ONLY ||
+        aPresence == DReport.PRESENT_IN_SECOND_ONLY,
+      "bad presence"
+    );
+
+    // If the process is empty, that means this process -- which is the main
+    // process, because this is chrome JS code -- is doing the dumping.
+    // Generate the process identifier: `Main Process (pid $PID)`.
+    //
+    // Note that `HandleReportAndFinishReportingCallbacks::Callback()` handles
+    // this when saving memory reports to file. So, if we are loading memory
+    // reports from file then `aProcess` will already be non-empty.
+    let process = aProcess
+      ? aProcess
+      : gMainProcessPrefix + " (pid " + Services.appinfo.processID + ")";
+
+    // Store the "resident" value for each process, so that if we filter it
+    // out, we can still use it to correctly sort processes and generate the
+    // process index.
+    let info = infoByProcess[process];
+    if (!info) {
+      info = infoByProcess[process] = {};
+    }
+    if (aUnsafePath == "resident") {
+      infoByProcess[process].resident = aAmount;
+    }
+
+    // Ignore reports that don't match the current filter.
+    if (!stringMatchesFilter(aUnsafePath, aFilter)) {
+      return;
+    }
+
+    let unsafeNames = aUnsafePath.split("/");
+    let unsafeName0 = unsafeNames[0];
+    let isDegenerate = unsafeNames.length === 1;
+
+    // Get the PColl table for the process, creating it if necessary.
+    let pcoll = pcollsByProcess[process];
+    if (!pcollsByProcess[process]) {
+      pcoll = pcollsByProcess[process] = new PColl();
+    }
+
+    // Get the root node, creating it if necessary.
+    let psubcoll = isDegenerate ? pcoll._degenerates : pcoll._trees;
+    let t = psubcoll[unsafeName0];
+    if (!t) {
+      t = psubcoll[unsafeName0] = new TreeNode(
+        unsafeName0,
+        aUnits,
+        isDegenerate
+      );
+    }
+
+    if (!isDegenerate) {
+      // Add any missing nodes in the tree implied by aUnsafePath, and fill in
+      // the properties that we can with a top-down traversal.
+      for (let i = 1; i < unsafeNames.length; i++) {
+        let unsafeName = unsafeNames[i];
+        let u = t.findKid(unsafeName);
+        if (!u) {
+          u = new TreeNode(unsafeName, aUnits, isDegenerate);
+          if (!t._kids) {
+            t._kids = [];
+          }
+          t._kids.push(u);
+        }
+        t = u;
+      }
+
+      // Update the heap total if necessary.
+      if (unsafeName0 === "explicit" && aKind == KIND_HEAP) {
+        pcollsByProcess[process]._heapTotal += aAmount;
+      }
+    }
+
+    if (t._amount) {
+      // Duplicate!  Sum the values and mark it as a dup.
+      t._amount += aAmount;
+      t._nMerged = t._nMerged ? t._nMerged + 1 : 2;
+      assert(t._presence === aPresence, "presence mismatch");
+    } else {
+      // New leaf node.  Fill in extra node details from the report.
+      t._amount = aAmount;
+      t._description = aDescription;
+      if (aPresence !== undefined) {
+        t._presence = aPresence;
+      }
+    }
+  }
+
+  function displayReports() {
+    // Sort the processes.
+    let processes = Object.keys(infoByProcess);
+    processes.sort(function(aProcessA, aProcessB) {
+      assert(
+        aProcessA != aProcessB,
+        `Elements of Object.keys() should be unique, but ` +
+          `saw duplicate '${aProcessA}' elem.`
+      );
+
+      // Always put the main process first.
+      if (aProcessA.startsWith(gMainProcessPrefix)) {
+        return -1;
+      }
+      if (aProcessB.startsWith(gMainProcessPrefix)) {
+        return 1;
+      }
+
+      // Then sort by resident size.
+      let residentA = infoByProcess[aProcessA].resident || -1;
+      let residentB = infoByProcess[aProcessB].resident || -1;
+      if (residentA > residentB) {
+        return -1;
+      }
+      if (residentA < residentB) {
+        return 1;
+      }
+
+      // Then sort by process name.
+      if (aProcessA < aProcessB) {
+        return -1;
+      }
+      if (aProcessA > aProcessB) {
+        return 1;
+      }
+
+      return 0;
+    });
+
+    // We set up this general layout inside gMain:
+    //
+    //   <div class="outputContainer">
+    //     <div class="sections"></div>
+    //     <div class="sidebar">
+    //       <div class="sidebarContents">
+    //         <div class="sidebarItem filterItem"></div>
+    //         <div class="sidebarItem indexItem"></div>
+    //       </div>
+    //     </div>
+    //   </div>
+    //
+    // If we detect that outputContainer already exists, then this is an update
+    // (due to typing in a filter string) to an already-displayed memory report.
+    // In this case we preserve the structure of the layout and only replace
+    // div.sections and #indexItem. Preserving the filter sidebar item means we
+    // preserve any editing state in its <input>.
+
+    // Generate the main process sections.
+    let sections = newElement("div", "sections");
+    sections.setAttribute("role", "main");
+
+    for (let [i, process] of processes.entries()) {
+      let pcolls = pcollsByProcess[process];
+      if (!pcolls) {
+        continue;
+      }
+
+      let section = appendElement(sections, "div", "section");
+      appendProcessAboutMemoryElements(
+        section,
+        i,
+        process,
+        pcolls._trees,
+        pcolls._degenerates,
+        pcolls._heapTotal,
+        aHasMozMallocUsableSize,
+        aFilter != ""
+      );
+    }
+
+    if (!sections.firstChild) {
+      appendElementWithText(sections, "div", "section", "No results found.");
+    }
+
+    // Generate the process index.
+    let indexItem = newElement("div", "sidebarItem");
+    indexItem.classList.add("indexItem");
+    appendElementWithText(indexItem, "div", "sidebarLabel", "Process index");
+    let indexList = appendElement(indexItem, "ul", "index");
+
+    for (let [i, process] of processes.entries()) {
+      let indexListItem = appendElement(indexList, "li");
+      let pcolls = pcollsByProcess[process];
+      if (pcolls) {
+        let indexLink = appendElementWithText(indexListItem, "a", "", process);
+        indexLink.href = "#start" + i;
+      } else {
+        // We've filtered out all reports from this process. Generate a non-link
+        // entry in the process index, and skip creating a process report
+        // section.
+        indexListItem.textContent = process;
+      }
+    }
+
+    // If we are updating, just swap in the new process output.
+    let outputContainer = gMain.querySelector(".outputContainer");
+    if (outputContainer) {
+      outputContainer.querySelector(".sections").replaceWith(sections);
+      outputContainer.querySelector(".indexItem").replaceWith(indexItem);
+      return;
+    }
+
+    // Otherwise, generate the rest of the layout.
+    outputContainer = appendElement(gMain, "div", "outputContainer");
+    outputContainer.appendChild(sections);
+
+    let sidebar = appendElement(outputContainer, "div", "sidebar");
+    sidebar.setAttribute("role", "navigation");
+    let sidebarContents = appendElement(sidebar, "div", "sidebarContents");
+
+    // Generate the filter input and checkbox.
+    let filterItem = appendElement(sidebarContents, "div", "sidebarItem");
+    filterItem.classList.add("filterItem");
+    appendElementWithText(filterItem, "div", "sidebarLabel", "Filter");
+
+    let filterInput = appendElement(filterItem, "input", "filterInput");
+    filterInput.placeholder = "Memory report path filter";
+
+    let filterOptions = appendElement(filterItem, "div");
+    let filterRegExLabel = appendElement(filterOptions, "label");
+    let filterRegExCheckbox = appendElement(filterRegExLabel, "input");
+    filterRegExCheckbox.type = "checkbox";
+    filterRegExLabel.append(" Regular expression");
+
+    // Set up event handlers to update the display if the filter input or
+    // checkbox changes.
+    let filterUpdateTimeout;
+    let filterUpdate = function() {
+      if (filterUpdateTimeout) {
+        window.clearTimeout(filterUpdateTimeout);
+      }
+      filterUpdateTimeout = window.setTimeout(function() {
+        try {
+          gFilter =
+            filterRegExCheckbox.checked && filterInput.value != ""
+              ? new RegExp(filterInput.value)
+              : filterInput.value;
+        } catch (ex) {
+          // Match nothing if the regex was invalid.
+          gFilter = new RegExp("^$");
+        }
+        updateAboutMemoryFromCurrentData();
+      }, gFilterUpdateDelayMS);
+    };
+    filterInput.oninput = filterUpdate;
+    filterRegExCheckbox.onchange = filterUpdate;
+
+    // Append the process list item after the filter item.
+    sidebarContents.appendChild(indexItem);
+  }
+
+  aProcessReports(handleReport, displayReports);
+}
+
+// ---------------------------------------------------------------------------
+
+// There are two kinds of TreeNode.
+// - Leaf TreeNodes correspond to reports.
+// - Non-leaf TreeNodes are just scaffolding nodes for the tree;  their values
+//   are derived from their children.
+// Some trees are "degenerate", i.e. they contain a single node, i.e. they
+// correspond to a report whose path has no '/' separators.
+function TreeNode(aUnsafeName, aUnits, aIsDegenerate) {
+  this._units = aUnits;
+  this._unsafeName = aUnsafeName;
+  if (aIsDegenerate) {
+    this._isDegenerate = true;
+  }
+
+  // Leaf TreeNodes have these properties added immediately after construction:
+  // - _amount
+  // - _description
+  // - _nMerged (only defined if > 1)
+  // - _presence (only defined if value is PRESENT_IN_{FIRST,SECOND}_ONLY)
+  //
+  // Non-leaf TreeNodes have these properties added later:
+  // - _kids
+  // - _amount
+  // - _description
+  // - _hideKids (only defined if true)
+  // - _maxAbsDescendant (on-demand, only when gIsDiff is set)
+}
+
+TreeNode.prototype = {
+  findKid(aUnsafeName) {
+    if (this._kids) {
+      for (let kid of this._kids) {
+        if (kid._unsafeName === aUnsafeName) {
+          return kid;
+        }
+      }
+    }
+    return undefined;
+  },
+
+  // When gIsDiff is false, tree operations -- sorting and determining if a
+  // sub-tree is significant -- are straightforward. But when gIsDiff is true,
+  // the combination of positive and negative values within a tree complicates
+  // things. So for a non-leaf node, instead of just looking at _amount, we
+  // instead look at the maximum absolute value of the node and all of its
+  // descendants.
+  maxAbsDescendant() {
+    if (!this._kids) {
+      // No kids? Just return the absolute value of the amount.
+      return Math.abs(this._amount);
+    }
+
+    if ("_maxAbsDescendant" in this) {
+      // We've computed this before? Return the saved value.
+      return this._maxAbsDescendant;
+    }
+
+    // Compute the maximum absolute value of all descendants.
+    let max = Math.abs(this._amount);
+    for (let kid of this._kids) {
+      max = Math.max(max, kid.maxAbsDescendant());
+    }
+    this._maxAbsDescendant = max;
+    return max;
+  },
+
+  toString() {
+    switch (this._units) {
+      case UNITS_BYTES:
+        return formatBytes(this._amount);
+      case UNITS_COUNT:
+      case UNITS_COUNT_CUMULATIVE:
+        return formatNum(this._amount);
+      case UNITS_PERCENTAGE:
+        return formatPercentage(this._amount);
+      default:
+        throw new Error(
+          "Invalid memory report(s): bad units in TreeNode.toString"
+        );
+    }
+  },
+};
+
+// Sort TreeNodes first by size, then by name.  The latter is important for the
+// about:memory tests, which need a predictable ordering of reporters which
+// have the same amount.
+TreeNode.compareAmounts = function(aA, aB) {
+  let a, b;
+  if (gIsDiff) {
+    a = aA.maxAbsDescendant();
+    b = aB.maxAbsDescendant();
+  } else {
+    a = aA._amount;
+    b = aB._amount;
+  }
+  if (a > b) {
+    return -1;
+  }
+  if (a < b) {
+    return 1;
+  }
+  return TreeNode.compareUnsafeNames(aA, aB);
+};
+
+TreeNode.compareUnsafeNames = function(aA, aB) {
+  return aA._unsafeName.localeCompare(aB._unsafeName);
+};
+
+/**
+ * Fill in the remaining properties for the specified tree in a bottom-up
+ * fashion.
+ *
+ * @param aRoot
+ *        The tree root.
+ */
+function fillInTree(aRoot) {
+  // Fill in the remaining properties bottom-up.
+  function fillInNonLeafNodes(aT) {
+    if (!aT._kids) {
+      // Leaf node.  Has already been filled in.
+    } else if (aT._kids.length === 1 && aT != aRoot) {
+      // Non-root, non-leaf node with one child.  Merge the child with the node
+      // to avoid redundant entries.
+      let kid = aT._kids[0];
+      let kidBytes = fillInNonLeafNodes(kid);
+      aT._unsafeName += "/" + kid._unsafeName;
+      if (kid._kids) {
+        aT._kids = kid._kids;
+      } else {
+        delete aT._kids;
+      }
+      aT._amount = kidBytes;
+      aT._description = kid._description;
+      if (kid._nMerged !== undefined) {
+        aT._nMerged = kid._nMerged;
+      }
+      assert(!aT._hideKids && !kid._hideKids, "_hideKids set when merging");
+    } else {
+      // Non-leaf node with multiple children.  Derive its _amount and
+      // _description entirely from its children...
+      let kidsBytes = 0;
+      for (let kid of aT._kids) {
+        kidsBytes += fillInNonLeafNodes(kid);
+      }
+
+      // ... except in one special case. When diffing two memory report sets,
+      // if one set has a node with children and the other has the same node
+      // but without children -- e.g. the first has "a/b/c" and "a/b/d", but
+      // the second only has "a/b" -- we need to add a fake node "a/b/(fake)"
+      // to the second to make the trees comparable. It's ugly, but it works.
+      if (
+        aT._amount !== undefined &&
+        (aT._presence === DReport.PRESENT_IN_FIRST_ONLY ||
+          aT._presence === DReport.PRESENT_IN_SECOND_ONLY)
+      ) {
+        aT._amount += kidsBytes;
+        let fake = new TreeNode("(fake child)", aT._units);
+        fake._presence = DReport.ADDED_FOR_BALANCE;
+        fake._amount = aT._amount - kidsBytes;
+        aT._kids.push(fake);
+        delete aT._presence;
+      } else {
+        assert(
+          aT._amount === undefined,
+          "_amount already set for non-leaf node"
+        );
+        aT._amount = kidsBytes;
+      }
+      aT._description = "The sum of all entries below this one.";
+    }
+    return aT._amount;
+  }
+
+  // cannotMerge is set because don't want to merge into a tree's root node.
+  fillInNonLeafNodes(aRoot);
+}
+
+/**
+ * Compute the "heap-unclassified" value and insert it into the "explicit"
+ * tree.
+ *
+ * @param aT
+ *        The "explicit" tree.
+ * @param aHeapAllocatedNode
+ *        The "heap-allocated" tree node.
+ * @param aHeapTotal
+ *        The sum of all explicit HEAP reports for this process.
+ * @return A boolean indicating if "heap-allocated" is known for the process.
+ */
+function addHeapUnclassifiedNode(aT, aHeapAllocatedNode, aHeapTotal) {
+  if (aHeapAllocatedNode === undefined) {
+    return false;
+  }
+
+  if (aT.findKid("heap-unclassified")) {
+    // heap-unclassified was already calculated, there's nothing left to do.
+    // This can happen when memory reports are exported from areweslimyet.com.
+    return true;
+  }
+
+  assert(aHeapAllocatedNode._isDegenerate, "heap-allocated is not degenerate");
+  let heapAllocatedBytes = aHeapAllocatedNode._amount;
+  let heapUnclassifiedT = new TreeNode("heap-unclassified", UNITS_BYTES);
+  heapUnclassifiedT._amount = heapAllocatedBytes - aHeapTotal;
+  heapUnclassifiedT._description =
+    "Memory not classified by a more specific report. This includes " +
+    "slop bytes due to internal fragmentation in the heap allocator " +
+    "(caused when the allocator rounds up request sizes).";
+  aT._kids.push(heapUnclassifiedT);
+  aT._amount += heapUnclassifiedT._amount;
+  return true;
+}
+
+/**
+ * Sort all kid nodes from largest to smallest, and insert aggregate nodes
+ * where appropriate.
+ *
+ * @param aTotalBytes
+ *        The size of the tree's root node.
+ * @param aT
+ *        The tree.
+ */
+function sortTreeAndInsertAggregateNodes(aTotalBytes, aT) {
+  const kSignificanceThresholdPerc = 1;
+
+  function isInsignificant(aT) {
+    if (gVerbose.checked) {
+      return false;
+    }
+
+    let perc = gIsDiff
+      ? (100 * aT.maxAbsDescendant()) / Math.abs(aTotalBytes)
+      : (100 * aT._amount) / aTotalBytes;
+    return perc < kSignificanceThresholdPerc;
+  }
+
+  if (!aT._kids) {
+    return;
+  }
+
+  aT._kids.sort(TreeNode.compareAmounts);
+
+  // If the first child is insignificant, they all are, and there's no point
+  // creating an aggregate node that lacks siblings.  Just set the parent's
+  // _hideKids property and process all children.
+  if (isInsignificant(aT._kids[0])) {
+    aT._hideKids = true;
+    for (let kid of aT._kids) {
+      sortTreeAndInsertAggregateNodes(aTotalBytes, kid);
+    }
+    return;
+  }
+
+  // Look at all children except the last one.
+  let i;
+  for (i = 0; i < aT._kids.length - 1; i++) {
+    if (isInsignificant(aT._kids[i])) {
+      // This child is below the significance threshold.  If there are other
+      // (smaller) children remaining, move them under an aggregate node.
+      let i0 = i;
+      let nAgg = aT._kids.length - i0;
+      // Create an aggregate node.  Inherit units from the parent;  everything
+      // in the tree should have the same units anyway (we test this later).
+      let aggT = new TreeNode(`(${nAgg} tiny)`, aT._units);
+      aggT._kids = [];
+      let aggBytes = 0;
+      for (; i < aT._kids.length; i++) {
+        aggBytes += aT._kids[i]._amount;
+        aggT._kids.push(aT._kids[i]);
+      }
+      aggT._hideKids = true;
+      aggT._amount = aggBytes;
+      aggT._description =
+        nAgg +
+        " sub-trees that are below the " +
+        kSignificanceThresholdPerc +
+        "% significance threshold.";
+      aT._kids.splice(i0, nAgg, aggT);
+      aT._kids.sort(TreeNode.compareAmounts);
+
+      // Process the moved children.
+      for (let kid of aggT._kids) {
+        sortTreeAndInsertAggregateNodes(aTotalBytes, kid);
+      }
+      return;
+    }
+
+    sortTreeAndInsertAggregateNodes(aTotalBytes, aT._kids[i]);
+  }
+
+  // The first n-1 children were significant.  Don't consider if the last child
+  // is significant;  there's no point creating an aggregate node that only has
+  // one child.  Just process it.
+  sortTreeAndInsertAggregateNodes(aTotalBytes, aT._kids[i]);
+}
+
+// Global variable indicating if we've seen any invalid values for this
+// process;  it holds the unsafePaths of any such reports.  It is reset for
+// each new process.
+let gUnsafePathsWithInvalidValuesForThisProcess = [];
+
+function appendWarningElements(
+  aP,
+  aHasKnownHeapAllocated,
+  aHasMozMallocUsableSize,
+  aFiltered
+) {
+  // These warnings may not make sense if the reporters they reference have been
+  // filtered out, so just skip them if we have a filter applied.
+  if (!aFiltered && !aHasKnownHeapAllocated && !aHasMozMallocUsableSize) {
+    appendElementWithText(
+      aP,
+      "p",
+      "",
+      "WARNING: the 'heap-allocated' memory reporter and the " +
+        "moz_malloc_usable_size() function do not work for this platform " +
+        "and/or configuration.  This means that 'heap-unclassified' is not " +
+        "shown and the 'explicit' tree shows much less memory than it should.\n\n"
+    );
+  } else if (!aFiltered && !aHasKnownHeapAllocated) {
+    appendElementWithText(
+      aP,
+      "p",
+      "",
+      "WARNING: the 'heap-allocated' memory reporter does not work for this " +
+        "platform and/or configuration. This means that 'heap-unclassified' " +
+        "is not shown and the 'explicit' tree shows less memory than it should.\n\n"
+    );
+  } else if (!aFiltered && !aHasMozMallocUsableSize) {
+    appendElementWithText(
+      aP,
+      "p",
+      "",
+      "WARNING: the moz_malloc_usable_size() function does not work for " +
+        "this platform and/or configuration.  This means that much of the " +
+        "heap-allocated memory is not measured by individual memory reporters " +
+        "and so will fall under 'heap-unclassified'.\n\n"
+    );
+  }
+
+  if (gUnsafePathsWithInvalidValuesForThisProcess.length) {
+    let div = appendElement(aP, "div");
+    appendElementWithText(
+      div,
+      "p",
+      "",
+      "WARNING: the following values are negative or unreasonably large.\n"
+    );
+
+    let ul = appendElement(div, "ul");
+    for (
+      let i = 0;
+      i < gUnsafePathsWithInvalidValuesForThisProcess.length;
+      i++
+    ) {
+      appendTextNode(ul, " ");
+      appendElementWithText(
+        ul,
+        "li",
+        "",
+        flipBackslashes(gUnsafePathsWithInvalidValuesForThisProcess[i]) + "\n"
+      );
+    }
+
+    appendElementWithText(
+      div,
+      "p",
+      "",
+      "This indicates a defect in one or more memory reporters.  The " +
+        "invalid values are highlighted.\n\n"
+    );
+    gUnsafePathsWithInvalidValuesForThisProcess = []; // reset for the next process
+  }
+}
+
+/**
+ * Appends the about:memory elements for a single process.
+ *
+ * @param aP
+ *        The parent DOM node.
+ * @param aN
+ *        The number of the process, starting at 0.
+ * @param aProcess
+ *        The name of the process.
+ * @param aTrees
+ *        The table of non-degenerate trees for this process.
+ * @param aDegenerates
+ *        The table of degenerate trees for this process.
+ * @param aHasMozMallocUsableSize
+ *        Boolean indicating if moz_malloc_usable_size works.
+ * @param aFiltered
+ *        Boolean indicating whether the reports were filtered.
+ * @return The generated text.
+ */
+function appendProcessAboutMemoryElements(
+  aP,
+  aN,
+  aProcess,
+  aTrees,
+  aDegenerates,
+  aHeapTotal,
+  aHasMozMallocUsableSize,
+  aFiltered
+) {
+  let appendLink = function(aHere, aThere, aArrow) {
+    let link = appendElementWithText(aP, "a", "upDownArrow", aArrow);
+    link.href = "#" + aThere + aN;
+    link.id = aHere + aN;
+    link.title = `Go to the ${aThere} of ${aProcess}`;
+    link.style = "text-decoration: none";
+
+    // This gives nice spacing when we copy and paste.
+    appendElementWithText(aP, "span", "", "\n");
+  };
+
+  appendElementWithText(aP, "h1", "", aProcess);
+  appendLink("start", "end", "↓");
+
+  // We'll fill this in later.
+  let warningsDiv = appendElement(aP, "div", "accuracyWarning");
+
+  // The explicit tree.
+  let hasExplicitTree;
+  let hasKnownHeapAllocated;
+  {
+    let treeName = "explicit";
+    let t = aTrees[treeName];
+    if (t) {
+      let pre = appendSectionHeader(aP, "Explicit Allocations");
+      hasExplicitTree = true;
+      fillInTree(t);
+      // Using the "heap-allocated" reporter here instead of
+      // nsMemoryReporterManager.heapAllocated goes against the usual pattern.
+      // But the "heap-allocated" node will go in the tree like the others, so
+      // we have to deal with it, and once we're dealing with it, it's easier
+      // to keep doing so rather than switching to the distinguished amount.
+      hasKnownHeapAllocated =
+        aDegenerates &&
+        addHeapUnclassifiedNode(t, aDegenerates["heap-allocated"], aHeapTotal);
+      sortTreeAndInsertAggregateNodes(t._amount, t);
+      t._description = explicitTreeDescription;
+      appendTreeElements(pre, t, aProcess, "");
+      delete aTrees[treeName];
+    }
+    appendTextNode(aP, "\n"); // gives nice spacing when we copy and paste
+  }
+
+  // Fill in and sort all the non-degenerate other trees.
+  let otherTrees = [];
+  for (let unsafeName in aTrees) {
+    let t = aTrees[unsafeName];
+    assert(!t._isDegenerate, "tree is degenerate");
+    fillInTree(t);
+    sortTreeAndInsertAggregateNodes(t._amount, t);
+    otherTrees.push(t);
+  }
+  otherTrees.sort(TreeNode.compareUnsafeNames);
+
+  // Get the length of the longest root value among the degenerate other trees,
+  // and sort them as well.
+  let otherDegenerates = [];
+  let maxStringLength = 0;
+  for (let unsafeName in aDegenerates) {
+    let t = aDegenerates[unsafeName];
+    assert(t._isDegenerate, "tree is not degenerate");
+    let length = t.toString().length;
+    if (length > maxStringLength) {
+      maxStringLength = length;
+    }
+    otherDegenerates.push(t);
+  }
+  otherDegenerates.sort(TreeNode.compareUnsafeNames);
+
+  // Now generate the elements, putting non-degenerate trees first.
+  if (otherTrees.length || otherDegenerates.length) {
+    let pre = appendSectionHeader(aP, "Other Measurements");
+    for (let t of otherTrees) {
+      appendTreeElements(pre, t, aProcess, "");
+      appendTextNode(pre, "\n"); // blank lines after non-degenerate trees
+    }
+    for (let t of otherDegenerates) {
+      let padText = "".padStart(maxStringLength - t.toString().length, " ");
+      appendTreeElements(pre, t, aProcess, padText);
+    }
+    appendTextNode(aP, "\n"); // gives nice spacing when we copy and paste
+  }
+
+  // Add any warnings about inaccuracies in the "explicit" tree due to platform
+  // limitations.  These must be computed after generating all the text.  The
+  // newlines give nice spacing if we copy+paste into a text buffer.
+  if (hasExplicitTree) {
+    appendWarningElements(
+      warningsDiv,
+      hasKnownHeapAllocated,
+      aHasMozMallocUsableSize,
+      aFiltered
+    );
+  }
+
+  appendElementWithText(aP, "h3", "", "End of " + aProcess);
+  appendLink("end", "start", "↑");
+}
+
+// The locale used when formatting a number as a human-readable string in any
+// format.
+const kStyleLocale = "en-US";
+
+// Used for UNITS_BYTES values that are printed as MiB.
+const kMBFormat = new Intl.NumberFormat(kStyleLocale, {
+  minimumFractionDigits: 2,
+  maximumFractionDigits: 2,
+});
+
+// Used for UNITS_PERCENTAGE values.
+const kPercFormatter = new Intl.NumberFormat(kStyleLocale, {
+  style: "percent",
+  minimumFractionDigits: 2,
+  maximumFractionDigits: 2,
+});
+
+// Used for fractions within the tree.
+const kFracFormatter = new Intl.NumberFormat(kStyleLocale, {
+  style: "percent",
+  minimumIntegerDigits: 2,
+  minimumFractionDigits: 2,
+  maximumFractionDigits: 2,
+});
+
+// Used for special-casing 100% fractions within the tree.
+const kFrac1Formatter = new Intl.NumberFormat(kStyleLocale, {
+  style: "percent",
+  minimumIntegerDigits: 3,
+  minimumFractionDigits: 1,
+  maximumFractionDigits: 1,
+});
+
+// Used when no custom formatting was requested.
+const kDefaultNumFormatter = new Intl.NumberFormat(kStyleLocale);
+
+/**
+ * Formats an int as a human-readable string.
+ *
+ * @param aN
+ *        The integer to format.
+ * @param aFormatter
+ *        Optional formatter object.
+ * @return A human-readable string representing the int.
+ */
+function formatNum(aN, aFormatter) {
+  return (aFormatter || kDefaultNumFormatter).format(aN);
+}
+
+/**
+ * Converts a byte count to an appropriate string representation.
+ *
+ * @param aBytes
+ *        The byte count.
+ * @return The string representation.
+ */
+function formatBytes(aBytes) {
+  return gVerbose.checked
+    ? `${formatNum(aBytes)} B`
+    : `${formatNum(aBytes / (1024 * 1024), kMBFormat)} MB`;
+}
+
+/**
+ * Converts a UNITS_PERCENTAGE value to an appropriate string representation.
+ *
+ * @param aPerc100x
+ *        The percentage, multiplied by 100 (see nsIMemoryReporter).
+ * @return The string representation
+ */
+function formatPercentage(aPerc100x) {
+  // A percentage like 12.34% will have an aPerc100x value of 1234, and we need
+  // to divide that by 10,000 to get the 0.1234 that toLocaleString() wants.
+  return formatNum(aPerc100x / 10000, kPercFormatter);
+}
+
+/*
+ * Converts a tree fraction to an appropriate string representation.
+ *
+ * @param aNum
+ *        The numerator.
+ * @param aDenom
+ *        The denominator.
+ * @return The string representation
+ */
+function formatTreeFrac(aNum, aDenom) {
+  // Two special behaviours here:
+  // - We treat 0 / 0 as 100%.
+  // - We want 4 digits, as much as possible, because it gives good vertical
+  //   alignment. For positive numbers, 00.00%--99.99% works straighforwardly,
+  //   but 100.0% needs special handling.
+  let num = aDenom === 0 ? 1 : aNum / aDenom;
+  return 0.99995 <= num && num <= 1
+    ? formatNum(1, kFrac1Formatter)
+    : formatNum(num, kFracFormatter);
+}
+
+const kNoKidsSep = " ── ",
+  kHideKidsSep = " ++ ",
+  kShowKidsSep = " -- ";
+
+function appendMrNameSpan(
+  aP,
+  aDescription,
+  aUnsafeName,
+  aIsInvalid,
+  aNMerged,
+  aPresence
+) {
+  let safeName = flipBackslashes(aUnsafeName);
+  if (!aIsInvalid && !aNMerged && !aPresence) {
+    safeName += "\n";
+  }
+  let nameSpan = appendElementWithText(aP, "span", "mrName", safeName);
+  nameSpan.title = aDescription;
+
+  if (aIsInvalid) {
+    let noteText = " [?!]";
+    if (!aNMerged) {
+      noteText += "\n";
+    }
+    let noteSpan = appendElementWithText(aP, "span", "mrNote", noteText);
+    noteSpan.title =
+      "Warning: this value is invalid and indicates a bug in one or more " +
+      "memory reporters. ";
+  }
+
+  if (aNMerged) {
+    let noteText = ` [${aNMerged}]`;
+    if (!aPresence) {
+      noteText += "\n";
+    }
+    let noteSpan = appendElementWithText(aP, "span", "mrNote", noteText);
+    noteSpan.title =
+      "This value is the sum of " +
+      aNMerged +
+      " memory reports that all have the same path.";
+  }
+
+  if (aPresence) {
+    let c, title;
+    switch (aPresence) {
+      case DReport.PRESENT_IN_FIRST_ONLY:
+        c = "-";
+        title =
+          "This value was only present in the first set of memory reports.";
+        break;
+      case DReport.PRESENT_IN_SECOND_ONLY:
+        c = "+";
+        title =
+          "This value was only present in the second set of memory reports.";
+        break;
+      case DReport.ADDED_FOR_BALANCE:
+        c = "!";
+        title =
+          "One of the sets of memory reports lacked children for this " +
+          "node's parent. This is a fake child node added to make the " +
+          "two memory sets comparable.";
+        break;
+      default:
+        assert(false, "bad presence");
+        break;
+    }
+    let noteSpan = appendElementWithText(aP, "span", "mrNote", ` [${c}]\n`);
+    noteSpan.title = title;
+  }
+}
+
+// This is used to record the (safe) IDs of which sub-trees have been manually
+// expanded (marked as true) and collapsed (marked as false).  It's used to
+// replicate the collapsed/expanded state when the page is updated.  It can end
+// up holding IDs of nodes that no longer exist, e.g. for compartments that
+// have been closed.  This doesn't seem like a big deal, because the number is
+// limited by the number of entries the user has changed from their original
+// state.
+let gShowSubtreesBySafeTreeId = {};
+
+function assertClassListContains(aElem, aClassName) {
+  assert(aElem, "undefined " + aClassName);
+  assert(aElem.classList.contains(aClassName), "classname isn't " + aClassName);
+}
+
+function toggle(aEvent) {
+  // This relies on each line being a span that contains at least four spans:
+  // mrValue, mrPerc, mrSep, mrName, and then zero or more mrNotes.  All
+  // whitespace must be within one of these spans for this function to find the
+  // right nodes.  And the span containing the children of this line must
+  // immediately follow.  Assertions check this.
+
+  // We want the outer span. |aEvent.target| will normally be one of the inner
+  // spans. However, if the click was dispatched via a11y, it might be the outer
+  // span because some of the inner spans are pruned from the a11y tree.
+  let outerSpan = aEvent.target.classList.contains("hasKids")
+    ? aEvent.target
+    : aEvent.target.parentNode;
+  assertClassListContains(outerSpan, "hasKids");
+
+  // Toggle the '++'/'--' separator.
+  let isExpansion;
+  let sepSpan = outerSpan.childNodes[2];
+  assertClassListContains(sepSpan, "mrSep");
+  if (sepSpan.textContent === kHideKidsSep) {
+    isExpansion = true;
+    sepSpan.textContent = kShowKidsSep;
+    outerSpan.setAttribute("aria-expanded", "true");
+  } else if (sepSpan.textContent === kShowKidsSep) {
+    isExpansion = false;
+    sepSpan.textContent = kHideKidsSep;
+    outerSpan.setAttribute("aria-expanded", "false");
+  } else {
+    assert(false, "bad sepSpan textContent");
+  }
+
+  // Toggle visibility of the span containing this node's children.
+  let subTreeSpan = outerSpan.nextSibling;
+  assertClassListContains(subTreeSpan, "kids");
+  subTreeSpan.classList.toggle("hidden");
+
+  // Record/unrecord that this sub-tree was toggled.
+  let safeTreeId = outerSpan.id;
+  if (gShowSubtreesBySafeTreeId[safeTreeId] !== undefined) {
+    delete gShowSubtreesBySafeTreeId[safeTreeId];
+  } else {
+    gShowSubtreesBySafeTreeId[safeTreeId] = isExpansion;
+  }
+}
+
+function expandPathToThisElement(aElement) {
+  if (aElement.classList.contains("kids")) {
+    // Unhide the kids.
+    aElement.classList.remove("hidden");
+    expandPathToThisElement(aElement.previousSibling); // hasKids
+  } else if (aElement.classList.contains("hasKids")) {
+    // Change the separator to '--'.
+    let sepSpan = aElement.childNodes[2];
+    assertClassListContains(sepSpan, "mrSep");
+    sepSpan.textContent = kShowKidsSep;
+    aElement.setAttribute("aria-expanded", "true");
+    expandPathToThisElement(aElement.parentNode.parentNode); // kids or pre.entries
+  } else {
+    assertClassListContains(aElement, "entries");
+  }
+}
+
+/**
+ * Appends the elements for the tree, including its heading.
+ *
+ * @param aP
+ *        The parent DOM node.
+ * @param aRoot
+ *        The tree root.
+ * @param aProcess
+ *        The process the tree corresponds to.
+ * @param aPadText
+ *        A string to pad the start of each entry.
+ */
+function appendTreeElements(aP, aRoot, aProcess, aPadText) {
+  /**
+   * Appends the elements for a particular tree, without a heading. There's a
+   * subset of the Unicode "light" box-drawing chars that is widely implemented
+   * in terminals, and this code sticks to that subset to maximize the chance
+   * that copying and pasting about:memory output to a terminal will work
+   * correctly.
+   *
+   * @param aP
+   *        The parent DOM node.
+   * @param aProcess
+   *        The process the tree corresponds to.
+   * @param aUnsafeNames
+   *        An array of the names forming the path to aT.
+   * @param aRoot
+   *        The root of the tree this sub-tree belongs to.
+   * @param aT
+   *        The tree.
+   * @param aTlThis
+   *        The treeline for this entry.
+   * @param aTlKids
+   *        The treeline for this entry's children.
+   * @param aParentStringLength
+   *        The length of the formatted byte count of the top node in the tree.
+   */
+  function appendTreeElements2(
+    aP,
+    aProcess,
+    aUnsafeNames,
+    aRoot,
+    aT,
+    aTlThis,
+    aTlKids,
+    aParentStringLength
+  ) {
+    function appendN(aS, aC, aN) {
+      for (let i = 0; i < aN; i++) {
+        aS += aC;
+      }
+      return aS;
+    }
+
+    // The entire entry including children needs to be treated as a list item
+    // for a11y purposes.
+    let p = document.createElement("span");
+    p.setAttribute("role", "listitem");
+    aP.appendChild(p);
+
+    // The tree line.  Indent more if this entry is narrower than its parent.
+    let valueText = aT.toString();
+    let extraTlLength = Math.max(aParentStringLength - valueText.length, 0);
+    if (extraTlLength > 0) {
+      aTlThis = appendN(aTlThis, "─", extraTlLength);
+      aTlKids = appendN(aTlKids, " ", extraTlLength);
+    }
+    let treeLine = appendElementWithText(p, "span", "treeline", aTlThis);
+    treeLine.setAttribute("aria-hidden", "true");
+
+    // Detect and record invalid values.  But not if gIsDiff is true, because
+    // we expect negative values in that case.
+    assertInput(
+      aRoot._units === aT._units,
+      "units within a tree are inconsistent"
+    );
+    let tIsInvalid = false;
+    if (!gIsDiff && !(0 <= aT._amount && aT._amount <= aRoot._amount)) {
+      tIsInvalid = true;
+      let unsafePath = aUnsafeNames.join("/");
+      gUnsafePathsWithInvalidValuesForThisProcess.push(unsafePath);
+      reportAssertionFailure(
+        `Invalid value (${aT._amount} / ${aRoot._amount}) for ` +
+          flipBackslashes(unsafePath)
+      );
+    }
+
+    // For non-leaf nodes, the entire sub-tree is put within a span so it can
+    // be collapsed if the node is clicked on.
+    let d;
+    let sep;
+    let showSubtrees;
+    if (aT._kids) {
+      // Determine if we should show the sub-tree below this entry;  this
+      // involves reinstating any previous toggling of the sub-tree.
+      let unsafePath = aUnsafeNames.join("/");
+      let safeTreeId = `${aProcess}:${flipBackslashes(unsafePath)}`;
+      showSubtrees = !aT._hideKids;
+      if (gShowSubtreesBySafeTreeId[safeTreeId] !== undefined) {
+        showSubtrees = gShowSubtreesBySafeTreeId[safeTreeId];
+      }
+      d = appendElement(p, "span", "hasKids");
+      d.id = safeTreeId;
+      d.onclick = toggle;
+      d.setAttribute("role", "button");
+      sep = showSubtrees ? kShowKidsSep : kHideKidsSep;
+      d.setAttribute("aria-expanded", showSubtrees ? "true" : "false");
+    } else {
+      assert(!aT._hideKids, "leaf node with _hideKids set");
+      sep = kNoKidsSep;
+      d = p;
+    }
+
+    // The value.
+    appendElementWithText(
+      d,
+      "span",
+      "mrValue" + (tIsInvalid ? " invalid" : ""),
+      valueText
+    );
+
+    // The percentage (omitted for single entries).
+    if (!aT._isDegenerate) {
+      let percText = formatTreeFrac(aT._amount, aRoot._amount);
+      appendElementWithText(d, "span", "mrPerc", ` (${percText})`);
+    }
+
+    // The separator.
+    appendElementWithText(d, "span", "mrSep", sep);
+
+    // The entry's name.
+    appendMrNameSpan(
+      d,
+      aT._description,
+      aT._unsafeName,
+      tIsInvalid,
+      aT._nMerged,
+      aT._presence
+    );
+
+    // In non-verbose mode, invalid nodes can be hidden in collapsed sub-trees.
+    // But it's good to always see them, so force this.
+    if (!gVerbose.checked && tIsInvalid) {
+      expandPathToThisElement(aT._kids ? d : aP);
+    }
+
+    // Recurse over children.
+    if (aT._kids) {
+      // The 'kids' class is just used for sanity checking in toggle().
+      d = appendElement(p, "span", showSubtrees ? "kids" : "kids hidden");
+      d.setAttribute("role", "list");
+
+      let tlThisForMost, tlKidsForMost;
+      if (aT._kids.length > 1) {
+        tlThisForMost = aTlKids + "├──";
+        tlKidsForMost = aTlKids + "│  ";
+      }
+      let tlThisForLast = aTlKids + "└──";
+      let tlKidsForLast = aTlKids + "   ";
+
+      for (let [i, kid] of aT._kids.entries()) {
+        let isLast = i == aT._kids.length - 1;
+        aUnsafeNames.push(kid._unsafeName);
+        appendTreeElements2(
+          d,
+          aProcess,
+          aUnsafeNames,
+          aRoot,
+          kid,
+          !isLast ? tlThisForMost : tlThisForLast,
+          !isLast ? tlKidsForMost : tlKidsForLast,
+          valueText.length
+        );
+        aUnsafeNames.pop();
+      }
+    }
+  }
+
+  let rootStringLength = aRoot.toString().length;
+  appendTreeElements2(
+    aP,
+    aProcess,
+    [aRoot._unsafeName],
+    aRoot,
+    aRoot,
+    aPadText,
+    aPadText,
+    rootStringLength
+  );
+}
+
+// ---------------------------------------------------------------------------
+
+function appendSectionHeader(aP, aText) {
+  appendElementWithText(aP, "h2", "", aText + "\n");
+  let entries = appendElement(aP, "pre", "entries");
+  entries.setAttribute("role", "list");
+  return entries;
+}
+
+// ---------------------------------------------------------------------------
+
+function saveReportsToFile() {
+  let fp = Cc["@mozilla.org/filepicker;1"].createInstance(Ci.nsIFilePicker);
+  fp.appendFilter("Zipped JSON files", "*.json.gz");
+  fp.appendFilters(Ci.nsIFilePicker.filterAll);
+  fp.filterIndex = 0;
+  fp.addToRecentDocs = true;
+  fp.defaultString = "memory-report.json.gz";
+
+  let fpFinish = function(aFile) {
+    let dumper = Cc["@mozilla.org/memory-info-dumper;1"].getService(
+      Ci.nsIMemoryInfoDumper
+    );
+    let finishDumping = () => {
+      updateMainAndFooter(
+        "Saved memory reports to " + aFile.path,
+        SHOW_TIMESTAMP,
+        HIDE_FOOTER
+      );
+    };
+    dumper.dumpMemoryReportsToNamedFile(
+      aFile.path,
+      finishDumping,
+      null,
+      gAnonymize.checked,
+      /* minimize memory usage = */ false
+    );
+  };
+
+  let fpCallback = function(aResult) {
+    if (
+      aResult == Ci.nsIFilePicker.returnOK ||
+      aResult == Ci.nsIFilePicker.returnReplace
+    ) {
+      fpFinish(fp.file);
+    }
+  };
+
+  try {
+    fp.init(window, "Save Memory Reports", Ci.nsIFilePicker.modeSave);
+  } catch (ex) {
+    // This will fail on Android, since there is no Save as file picker there.
+    // Just save to the default downloads dir if it does.
+    Downloads.getSystemDownloadsDirectory().then(function(aDirPath) {
+      let file = FileUtils.File(aDirPath);
+      file.append(fp.defaultString);
+      fpFinish(file);
+    });
+
+    return;
+  }
+  fp.open(fpCallback);
+}
diff --git a/toolkit/components/aboutmemory/content/aboutMemory.xhtml b/toolkit/components/aboutmemory/content/aboutMemory.xhtml
new file mode 100644
index 0000000000..99955b445a
--- /dev/null
+++ b/toolkit/components/aboutmemory/content/aboutMemory.xhtml
@@ -0,0 +1,28 @@
+<?xml version="1.0"?>
+
+<!-- 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/. -->
+
+<!-- We explicitly set the language to English, which more-or-less guarantees
+     that the box-drawing characters used are the correct width. Without that,
+     in a Japanese or Chinese locale we might end up with box-drawing
+     characters that are twice the width of English characters, which messes up
+     the tree layout. See bug 1561153 for details. Note that about:memory is
+     not localized, so setting it explicitly to English should be fine.
+
+     We also set the fonts in aboutMemory.css in such a way that maximizes the
+     chances that the font chosen supports the box-drawing chars.
+-->
+<html xmlns="http://www.w3.org/1999/xhtml" lang="en">
+  <head>
+    <meta http-equiv="Content-Security-Policy" content="default-src chrome:; object-src 'none'" />
+    <meta name="viewport" content="width=device-width"/>
+    <meta name="color-scheme" content="light dark"/>
+    <title>Memory Analyzer</title>
+    <link rel="stylesheet" href="chrome://global/skin/aboutMemory.css" type="text/css"/>
+    <script src="chrome://global/content/aboutMemory.js"/>
+  </head>
+
+  <body></body>
+</html>