Adding upstream version 110.0.1.upstream/110.0.1upstream

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

46 files changed, 7161 insertions, 0 deletions

diff --git a/browser/components/downloads/test/browser/blank.JPG b/browser/components/downloads/test/browser/blank.JPG
new file mode 100644
index 0000000000..1cda9a53dc
--- /dev/null
+++ b/browser/components/downloads/test/browser/blank.JPG
diff --git a/browser/components/downloads/test/browser/browser.ini b/browser/components/downloads/test/browser/browser.ini
new file mode 100644
index 0000000000..6c5c0ec1d0
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser.ini
@@ -0,0 +1,64 @@
+[DEFAULT]
+support-files = head.js
+
+[browser_about_downloads.js]
+[browser_basic_functionality.js]
+[browser_download_overwrite.js]
+support-files =
+  foo.txt
+  foo.txt^headers^
+  !/toolkit/content/tests/browser/common/mockTransfer.js
+[browser_download_starts_in_tmp.js]
+[browser_first_download_panel.js]
+skip-if =
+  os == "linux" # Bug 949434
+[browser_image_mimetype_issues.js]
+https_first_disabled = true
+support-files =
+  not-really-a-jpeg.jpeg
+  not-really-a-jpeg.jpeg^headers^
+  blank.JPG
+[browser_library_select_all.js]
+[browser_overflow_anchor.js]
+skip-if = os == "linux" # Bug 952422
+[browser_confirm_unblock_download.js]
+[browser_iframe_gone_mid_download.js]
+[browser_indicatorDrop.js]
+[browser_libraryDrop.js]
+skip-if = (os == 'win' && os_version == '10.0' && ccov) # Bug 1306510
+[browser_library_clearall.js]
+[browser_download_opens_on_click.js]
+[browser_download_opens_policy.js]
+[browser_download_spam_protection.js]
+skip-if =
+  os == "linux" && bits == 64 # bug 1743263 & Bug 1742678
+  os == "win" && os_version == "6.1" # Skip on Azure - frequent failure
+support-files = test_spammy_page.html
+[browser_download_is_clickable.js]
+[browser_downloads_keynav.js]
+[browser_downloads_panel_block.js]
+[browser_downloads_panel_context_menu.js]
+skip-if =
+  os == "win" && os_version == "10.0" && bits == 64 && !debug # Bug 1719949
+  win10_2004 && bits == 32 && debug # Bug 1727925
+[browser_downloads_context_menu_always_open_similar_files.js]
+[browser_downloads_panel_ctrl_click.js]
+[browser_downloads_panel_disable_items.js]
+support-files =
+  foo.txt
+  foo.txt^headers^
+[browser_downloads_panel_dontshow.js]
+[browser_downloads_panel_height.js]
+[browser_downloads_panel_opens.js]
+skip-if =
+  os == "linux" && verify && !debug # For some reason linux opt verify builds time out.
+support-files =
+  foo.txt
+  foo.txt^headers^
+[browser_downloads_autohide.js]
+[browser_go_to_download_page.js]
+[browser_pdfjs_preview.js]
+[browser_downloads_pauseResume.js]
+[browser_downloads_panel_focus.js]
+[browser_downloads_context_menu_delete_file.js]
+[browser_tempfilename.js]
diff --git a/browser/components/downloads/test/browser/browser_about_downloads.js b/browser/components/downloads/test/browser/browser_about_downloads.js
new file mode 100644
index 0000000000..ed3bebf12f
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_about_downloads.js
@@ -0,0 +1,44 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+/**
+ * Ensure about:downloads actually works.
+ */
+add_task(async function test_about_downloads() {
+  await task_resetState();
+  registerCleanupFunction(task_resetState);
+
+  await setDownloadDir();
+
+  await task_addDownloads([
+    { state: DownloadsCommon.DOWNLOAD_FINISHED },
+    { state: DownloadsCommon.DOWNLOAD_PAUSED },
+  ]);
+
+  await BrowserTestUtils.withNewTab("about:blank", async browser => {
+    let downloadsLoaded = BrowserTestUtils.waitForEvent(
+      browser,
+      "InitialDownloadsLoaded",
+      true
+    );
+    BrowserTestUtils.loadURI(browser, "about:downloads");
+    await downloadsLoaded;
+    await SpecialPowers.spawn(browser, [], async function() {
+      let box = content.document.getElementById("downloadsListBox");
+      ok(box, "Should have list of downloads");
+      is(box.children.length, 2, "Should have 2 downloads.");
+      for (let kid of box.children) {
+        let desc = kid.querySelector(".downloadTarget");
+        // This would just be an `is` check, but stray temp files
+        // if this test (or another in this dir) ever fails could throw that off.
+        ok(
+          /^dm-ui-test(-\d+)?.file$/.test(desc.value),
+          `Label '${desc.value}' should match 'dm-ui-test.file'`
+        );
+      }
+      ok(box.firstChild.selected, "First item should be selected.");
+    });
+  });
+});
diff --git a/browser/components/downloads/test/browser/browser_basic_functionality.js b/browser/components/downloads/test/browser/browser_basic_functionality.js
new file mode 100644
index 0000000000..7e58f95fca
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_basic_functionality.js
@@ -0,0 +1,59 @@
+/* -*- indent-tabs-mode: nil; js-indent-level: 2 -*- */
+/* vim: set ts=2 et sw=2 tw=80: */
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+registerCleanupFunction(async function() {
+  await task_resetState();
+});
+
+/**
+ * Make sure the downloads panel can display items in the right order and
+ * contains the expected data.
+ */
+add_task(async function test_basic_functionality() {
+  // Display one of each download state.
+  const DownloadData = [
+    { state: DownloadsCommon.DOWNLOAD_NOTSTARTED },
+    { state: DownloadsCommon.DOWNLOAD_PAUSED },
+    { state: DownloadsCommon.DOWNLOAD_FINISHED },
+    { state: DownloadsCommon.DOWNLOAD_FAILED },
+    { state: DownloadsCommon.DOWNLOAD_CANCELED },
+  ];
+
+  // Wait for focus first
+  await promiseFocus();
+
+  // Ensure that state is reset in case previous tests didn't finish.
+  await task_resetState();
+
+  // For testing purposes, show all the download items at once.
+  var originalCountLimit = DownloadsView.kItemCountLimit;
+  DownloadsView.kItemCountLimit = DownloadData.length;
+  registerCleanupFunction(function() {
+    DownloadsView.kItemCountLimit = originalCountLimit;
+  });
+
+  // Populate the downloads database with the data required by this test.
+  await task_addDownloads(DownloadData);
+
+  // Open the user interface and wait for data to be fully loaded.
+  await task_openPanel();
+
+  // Test item data and count.  This also tests the ordering of the display.
+  let richlistbox = document.getElementById("downloadsListBox");
+  /* disabled for failing intermittently (bug 767828)
+    is(richlistbox.itemChildren.length, DownloadData.length,
+       "There is the correct number of richlistitems");
+  */
+  let itemCount = richlistbox.itemChildren.length;
+  for (let i = 0; i < itemCount; i++) {
+    let element = richlistbox.itemChildren[itemCount - i - 1];
+    let download = DownloadsView.itemForElement(element).download;
+    is(
+      DownloadsCommon.stateOfDownload(download),
+      DownloadData[i].state,
+      "Download states match up"
+    );
+  }
+});
diff --git a/browser/components/downloads/test/browser/browser_confirm_unblock_download.js b/browser/components/downloads/test/browser/browser_confirm_unblock_download.js
new file mode 100644
index 0000000000..d88fa9a0e5
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_confirm_unblock_download.js
@@ -0,0 +1,110 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests the dialog which allows the user to unblock a downloaded file.
+
+registerCleanupFunction(() => {});
+
+async function assertDialogResult({ args, buttonToClick, expectedResult }) {
+  let promise = BrowserTestUtils.promiseAlertDialog(buttonToClick);
+  is(
+    await DownloadsCommon.confirmUnblockDownload(args),
+    expectedResult,
+    `Expect ${expectedResult} from ${buttonToClick}`
+  );
+  await promise;
+}
+
+/**
+ * Tests the "unblock" dialog, for each of the possible verdicts.
+ */
+add_task(async function test_unblock_dialog_unblock() {
+  for (let verdict of [
+    Downloads.Error.BLOCK_VERDICT_MALWARE,
+    Downloads.Error.BLOCK_VERDICT_POTENTIALLY_UNWANTED,
+    Downloads.Error.BLOCK_VERDICT_INSECURE,
+    Downloads.Error.BLOCK_VERDICT_UNCOMMON,
+  ]) {
+    let args = { verdict, window, dialogType: "unblock" };
+
+    // Test both buttons.
+    await assertDialogResult({
+      args,
+      buttonToClick: "accept",
+      expectedResult: "unblock",
+    });
+    await assertDialogResult({
+      args,
+      buttonToClick: "cancel",
+      expectedResult: "cancel",
+    });
+  }
+});
+
+/**
+ * Tests the "chooseUnblock" dialog for potentially unwanted downloads.
+ */
+add_task(async function test_chooseUnblock_dialog() {
+  for (let verdict of [
+    Downloads.Error.BLOCK_VERDICT_POTENTIALLY_UNWANTED,
+    Downloads.Error.BLOCK_VERDICT_INSECURE,
+  ]) {
+    let args = {
+      verdict,
+      window,
+      dialogType: "chooseUnblock",
+    };
+
+    // Test each of the three buttons.
+    await assertDialogResult({
+      args,
+      buttonToClick: "accept",
+      expectedResult: "unblock",
+    });
+    await assertDialogResult({
+      args,
+      buttonToClick: "cancel",
+      expectedResult: "cancel",
+    });
+    await assertDialogResult({
+      args,
+      buttonToClick: "extra1",
+      expectedResult: "confirmBlock",
+    });
+  }
+});
+
+/**
+ * Tests the "chooseOpen" dialog for uncommon downloads.
+ */
+add_task(async function test_chooseOpen_dialog() {
+  for (let verdict of [
+    Downloads.Error.BLOCK_VERDICT_UNCOMMON,
+    Downloads.Error.BLOCK_VERDICT_INSECURE,
+  ]) {
+    let args = {
+      verdict,
+      window,
+      dialogType: "chooseOpen",
+    };
+
+    // Test each of the three buttons.
+    await assertDialogResult({
+      args,
+      buttonToClick: "accept",
+      expectedResult: "open",
+    });
+    await assertDialogResult({
+      args,
+      buttonToClick: "cancel",
+      expectedResult: "cancel",
+    });
+    await assertDialogResult({
+      args,
+      buttonToClick: "extra1",
+      expectedResult: "confirmBlock",
+    });
+  }
+});
diff --git a/browser/components/downloads/test/browser/browser_download_is_clickable.js b/browser/components/downloads/test/browser/browser_download_is_clickable.js
new file mode 100644
index 0000000000..f3f2665010
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_download_is_clickable.js
@@ -0,0 +1,81 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+ChromeUtils.defineESModuleGetters(this, {
+  DownloadsViewUI: "resource:///modules/DownloadsViewUI.sys.mjs",
+});
+
+const { TelemetryTestUtils } = ChromeUtils.importESModule(
+  "resource://testing-common/TelemetryTestUtils.sys.mjs"
+);
+
+add_task(async function test_download_clickable() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["browser.download.improvements_to_download_panel", true]],
+  });
+  Services.telemetry.clearScalars();
+
+  startServer();
+  mustInterruptResponses();
+  let download = await promiseInterruptibleDownload();
+  let publicList = await Downloads.getList(Downloads.PUBLIC);
+  await publicList.add(download);
+
+  registerCleanupFunction(async function() {
+    await task_resetState();
+    Services.telemetry.clearScalars();
+  });
+
+  download.start();
+
+  await promiseDownloadHasProgress(download, 50);
+
+  await task_openPanel();
+
+  let listbox = document.getElementById("downloadsListBox");
+  ok(listbox, "Download list box present");
+
+  await TestUtils.waitForCondition(() => {
+    return listbox.childElementCount == 1;
+  });
+
+  info("All downloads show in the listbox.itemChildren ", listbox.itemChildren);
+
+  ok(
+    listbox.itemChildren[0].classList.contains("openWhenFinished"),
+    "Download should have clickable style when in progress"
+  );
+
+  ok(!download.launchWhenSucceeded, "launchWhenSucceeded should set to false");
+
+  ok(!download._launchedFromPanel, "LaunchFromPanel should set to false");
+
+  EventUtils.synthesizeMouseAtCenter(listbox.itemChildren[0], {});
+  ok(
+    download.launchWhenSucceeded,
+    "Should open the file when download is finished"
+  );
+  ok(download._launchedFromPanel, "File was scheduled to launch from panel");
+
+  EventUtils.synthesizeMouseAtCenter(listbox.itemChildren[0], {});
+
+  ok(
+    !download.launchWhenSucceeded,
+    "Should NOT open the file when download is finished"
+  );
+
+  ok(!download._launchedFromPanel, "File launch from panel was reset");
+
+  continueResponses();
+  await download.refresh();
+  await promiseDownloadHasProgress(download, 100);
+
+  TelemetryTestUtils.assertScalar(
+    TelemetryTestUtils.getProcessScalars("parent"),
+    "downloads.file_opened",
+    undefined,
+    "File opened from panel should not be incremented"
+  );
+});
diff --git a/browser/components/downloads/test/browser/browser_download_opens_on_click.js b/browser/components/downloads/test/browser/browser_download_opens_on_click.js
new file mode 100644
index 0000000000..49d80063cf
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_download_opens_on_click.js
@@ -0,0 +1,96 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+ChromeUtils.defineESModuleGetters(this, {
+  DownloadsViewUI: "resource:///modules/DownloadsViewUI.sys.mjs",
+});
+
+const { TelemetryTestUtils } = ChromeUtils.importESModule(
+  "resource://testing-common/TelemetryTestUtils.sys.mjs"
+);
+
+const { DownloadIntegration } = ChromeUtils.importESModule(
+  "resource://gre/modules/DownloadIntegration.sys.mjs"
+);
+
+add_task(async function test_download_opens_on_click() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["browser.download.improvements_to_download_panel", true]],
+  });
+  Services.telemetry.clearScalars();
+
+  startServer();
+  mustInterruptResponses();
+  let download = await promiseInterruptibleDownload();
+  let publicList = await Downloads.getList(Downloads.PUBLIC);
+  await publicList.add(download);
+
+  let oldLaunchFile = DownloadIntegration.launchFile;
+
+  let waitForLaunchFileCalled = new Promise(resolve => {
+    DownloadIntegration.launchFile = () => {
+      ok(true, "The file should be launched with an external application");
+      resolve();
+    };
+  });
+
+  registerCleanupFunction(async function() {
+    DownloadIntegration.launchFile = oldLaunchFile;
+    await task_resetState();
+    Services.telemetry.clearScalars();
+  });
+
+  TelemetryTestUtils.assertScalar(
+    TelemetryTestUtils.getProcessScalars("parent"),
+    "downloads.file_opened",
+    undefined,
+    "File opened from panel should not be initialized"
+  );
+
+  download.start();
+
+  await promiseDownloadHasProgress(download, 50);
+
+  await task_openPanel();
+
+  let listbox = document.getElementById("downloadsListBox");
+  ok(listbox, "Download list box present");
+
+  await TestUtils.waitForCondition(() => {
+    return listbox.childElementCount == 1;
+  });
+
+  info("All downloads show in the listbox.itemChildren ", listbox.itemChildren);
+
+  ok(
+    listbox.itemChildren[0].classList.contains("openWhenFinished"),
+    "Download should have clickable style when in progress"
+  );
+
+  ok(!download.launchWhenSucceeded, "launchWhenSucceeded should set to false");
+
+  ok(!download._launchedFromPanel, "LaunchFromPanel should set to false");
+
+  EventUtils.synthesizeMouseAtCenter(listbox.itemChildren[0], {});
+
+  ok(
+    download.launchWhenSucceeded,
+    "Should open the file when download is finished"
+  );
+  ok(download._launchedFromPanel, "File was scheduled to launch from panel");
+
+  continueResponses();
+  await download.refresh();
+  await promiseDownloadHasProgress(download, 100);
+
+  await waitForLaunchFileCalled;
+
+  TelemetryTestUtils.assertScalar(
+    TelemetryTestUtils.getProcessScalars("parent"),
+    "downloads.file_opened",
+    1,
+    "File opened from panel should be incremented"
+  );
+});
diff --git a/browser/components/downloads/test/browser/browser_download_opens_policy.js b/browser/components/downloads/test/browser/browser_download_opens_policy.js
new file mode 100644
index 0000000000..ab347f50b0
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_download_opens_policy.js
@@ -0,0 +1,111 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const { EnterprisePolicyTesting } = ChromeUtils.importESModule(
+  "resource://testing-common/EnterprisePolicyTesting.sys.mjs"
+);
+
+ChromeUtils.defineESModuleGetters(this, {
+  DownloadsViewUI: "resource:///modules/DownloadsViewUI.sys.mjs",
+});
+
+const { TelemetryTestUtils } = ChromeUtils.importESModule(
+  "resource://testing-common/TelemetryTestUtils.sys.mjs"
+);
+
+const { DownloadIntegration } = ChromeUtils.importESModule(
+  "resource://gre/modules/DownloadIntegration.sys.mjs"
+);
+
+add_task(async function test_download_opens_on_click() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["browser.download.improvements_to_download_panel", true]],
+  });
+  Services.telemetry.clearScalars();
+
+  await EnterprisePolicyTesting.setupPolicyEngineWithJson({
+    policies: {
+      ExemptDomainFileTypePairsFromFileTypeDownloadWarnings: [
+        {
+          file_extension: "jnlp",
+          domains: ["localhost"],
+        },
+      ],
+    },
+  });
+
+  startServer();
+  mustInterruptResponses();
+  let download = await promiseInterruptibleDownload(".jnlp");
+  let publicList = await Downloads.getList(Downloads.PUBLIC);
+  await publicList.add(download);
+
+  let oldLaunchFile = DownloadIntegration.launchFile;
+
+  let waitForLaunchFileCalled = new Promise(resolve => {
+    DownloadIntegration.launchFile = () => {
+      ok(true, "The file should be launched with an external application");
+      resolve();
+    };
+  });
+
+  registerCleanupFunction(async function() {
+    DownloadIntegration.launchFile = oldLaunchFile;
+    await task_resetState();
+    Services.telemetry.clearScalars();
+  });
+
+  TelemetryTestUtils.assertScalar(
+    TelemetryTestUtils.getProcessScalars("parent"),
+    "downloads.file_opened",
+    undefined,
+    "File opened from panel should not be initialized"
+  );
+
+  download.start();
+
+  await promiseDownloadHasProgress(download, 50);
+
+  await task_openPanel();
+
+  let listbox = document.getElementById("downloadsListBox");
+  ok(listbox, "Download list box present");
+
+  await TestUtils.waitForCondition(() => {
+    return listbox.childElementCount == 1;
+  });
+
+  info("All downloads show in the listbox.itemChildren ", listbox.itemChildren);
+
+  ok(
+    listbox.itemChildren[0].classList.contains("openWhenFinished"),
+    "Download should have clickable style when in progress"
+  );
+
+  ok(!download.launchWhenSucceeded, "launchWhenSucceeded should set to false");
+
+  ok(!download._launchedFromPanel, "LaunchFromPanel should set to false");
+
+  EventUtils.synthesizeMouseAtCenter(listbox.itemChildren[0], {});
+
+  ok(
+    download.launchWhenSucceeded,
+    "Should open the file when download is finished"
+  );
+  ok(download._launchedFromPanel, "File was scheduled to launch from panel");
+
+  continueResponses();
+  await download.refresh();
+  await promiseDownloadHasProgress(download, 100);
+
+  await waitForLaunchFileCalled;
+
+  TelemetryTestUtils.assertScalar(
+    TelemetryTestUtils.getProcessScalars("parent"),
+    "downloads.file_opened",
+    1,
+    "File opened from panel should be incremented"
+  );
+});
diff --git a/browser/components/downloads/test/browser/browser_download_overwrite.js b/browser/components/downloads/test/browser/browser_download_overwrite.js
new file mode 100644
index 0000000000..247542691d
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_download_overwrite.js
@@ -0,0 +1,128 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const TEST_ROOT = getRootDirectory(gTestPath).replace(
+  "chrome://mochitests/content",
+  "http://example.com"
+);
+
+var MockFilePicker = SpecialPowers.MockFilePicker;
+MockFilePicker.init(window);
+
+/* import-globals-from ../../../../../toolkit/content/tests/browser/common/mockTransfer.js */
+Services.scriptloader.loadSubScript(
+  "chrome://mochitests/content/browser/toolkit/content/tests/browser/common/mockTransfer.js",
+  this
+);
+
+add_setup(async function() {
+  // head.js has helpers that write to a nice unique file we can use.
+  await createDownloadedFile(gTestTargetFile.path, "Hello.\n");
+  ok(gTestTargetFile.exists(), "We created a test file.");
+
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["browser.download.improvements_to_download_panel", true],
+      ["browser.download.always_ask_before_handling_new_types", false],
+      ["browser.download.useDownloadDir", false],
+    ],
+  });
+  // Set up the file picker.
+  let destDir = gTestTargetFile.parent;
+
+  MockFilePicker.displayDirectory = destDir;
+  MockFilePicker.showCallback = function(fp) {
+    MockFilePicker.setFiles([gTestTargetFile]);
+    return MockFilePicker.returnOK;
+  };
+  registerCleanupFunction(function() {
+    MockFilePicker.cleanup();
+    if (gTestTargetFile.exists()) {
+      gTestTargetFile.remove(false);
+    }
+  });
+});
+
+// If we download a file and the user accepts overwriting an existing one,
+// we shouldn't first delete that file before moving the .part file into
+// place.
+add_task(async function test_overwrite_does_not_delete_first() {
+  let unregisteredTransfer = false;
+  let transferCompletePromise = new Promise(resolve => {
+    mockTransferCallback = resolve;
+  });
+  mockTransferRegisterer.register();
+
+  registerCleanupFunction(function() {
+    if (!unregisteredTransfer) {
+      mockTransferRegisterer.unregister();
+    }
+  });
+
+  // Now try and download a thing to the file:
+  await BrowserTestUtils.withNewTab(
+    {
+      gBrowser,
+      opening: TEST_ROOT + "foo.txt",
+      waitForLoad: false,
+      waitForStateStop: true,
+    },
+    async function() {
+      ok(await transferCompletePromise, "download should succeed");
+      ok(
+        gTestTargetFile.exists(),
+        "File should still exist and not have been deleted."
+      );
+      // Note: the download transfer is fake so data won't have been written to
+      // the file, so we can't verify that the download actually overwrites data
+      // like this.
+      mockTransferRegisterer.unregister();
+      unregisteredTransfer = true;
+    }
+  );
+});
+
+// If we download a file and the user accepts overwriting an existing one,
+// we should successfully overwrite its contents.
+add_task(async function test_overwrite_works() {
+  let publicDownloads = await Downloads.getList(Downloads.PUBLIC);
+  // First ensure we catch the download finishing.
+  let downloadFinishedPromise = new Promise(resolve => {
+    publicDownloads.addView({
+      onDownloadChanged(download) {
+        info("Download changed!");
+        if (download.succeeded || download.error) {
+          info("Download succeeded or errored");
+          publicDownloads.removeView(this);
+          publicDownloads.removeFinished();
+          resolve(download);
+        }
+      },
+    });
+  });
+  // Now try and download a thing to the file:
+  await BrowserTestUtils.withNewTab(
+    {
+      gBrowser,
+      opening: TEST_ROOT + "foo.txt",
+      waitForLoad: false,
+      waitForStateStop: true,
+    },
+    async function() {
+      info("wait for download to finish");
+      let download = await downloadFinishedPromise;
+      ok(download.succeeded, "Download should succeed");
+      ok(
+        gTestTargetFile.exists(),
+        "File should still exist and not have been deleted."
+      );
+      let contents = new TextDecoder().decode(
+        await IOUtils.read(gTestTargetFile.path)
+      );
+      info("Got: " + contents);
+      ok(contents.startsWith("Dummy"), "The file was overwritten.");
+    }
+  );
+});
diff --git a/browser/components/downloads/test/browser/browser_download_spam_protection.js b/browser/components/downloads/test/browser/browser_download_spam_protection.js
new file mode 100644
index 0000000000..f34d612b46
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_download_spam_protection.js
@@ -0,0 +1,225 @@
+/* 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 strict";
+
+var { XPCOMUtils } = ChromeUtils.importESModule(
+  "resource://gre/modules/XPCOMUtils.sys.mjs"
+);
+
+ChromeUtils.defineESModuleGetters(this, {
+  DownloadSpamProtection: "resource:///modules/DownloadSpamProtection.sys.mjs",
+});
+
+XPCOMUtils.defineLazyModuleGetters(this, {
+  BrowserWindowTracker: "resource:///modules/BrowserWindowTracker.jsm",
+  PermissionTestUtils: "resource://testing-common/PermissionTestUtils.jsm",
+});
+
+const TEST_URI = "https://example.com";
+
+const TEST_PATH = getRootDirectory(gTestPath).replace(
+  "chrome://mochitests/content",
+  TEST_URI
+);
+
+add_setup(async function() {
+  // Create temp directory
+  let time = new Date().getTime();
+  let tempDir = Services.dirsvc.get("TmpD", Ci.nsIFile);
+  tempDir.append(time);
+  Services.prefs.setIntPref("browser.download.folderList", 2);
+  Services.prefs.setComplexValue("browser.download.dir", Ci.nsIFile, tempDir);
+
+  PermissionTestUtils.add(
+    TEST_URI,
+    "automatic-download",
+    Services.perms.UNKNOWN_ACTION
+  );
+  await SpecialPowers.pushPrefEnv({
+    set: [["browser.download.enable_spam_prevention", true]],
+    clear: [
+      ["browser.download.improvements_to_download_panel"],
+      ["browser.download.alwaysOpenPanel"],
+      ["browser.download.always_ask_before_handling_new_types"],
+    ],
+  });
+
+  registerCleanupFunction(async () => {
+    Services.prefs.clearUserPref("browser.download.folderList");
+    Services.prefs.clearUserPref("browser.download.dir");
+    await IOUtils.remove(tempDir.path, { recursive: true });
+  });
+});
+
+add_task(async function check_download_spam_ui() {
+  await task_resetState();
+
+  let browserWin = BrowserWindowTracker.getTopWindow();
+  registerCleanupFunction(async () => {
+    for (let win of [browserWin, browserWin2]) {
+      win.DownloadsPanel.hidePanel();
+      DownloadIntegration.downloadSpamProtection.removeDownloadSpamForWindow(
+        TEST_URI,
+        win
+      );
+    }
+    let publicList = await Downloads.getList(Downloads.PUBLIC);
+    await publicList.removeFinished();
+    BrowserTestUtils.removeTab(newTab);
+    await BrowserTestUtils.closeWindow(browserWin2);
+  });
+  let observedBlockedDownloads = 0;
+  let gotAllBlockedDownloads = TestUtils.topicObserved(
+    "blocked-automatic-download",
+    () => {
+      return ++observedBlockedDownloads >= 99;
+    }
+  );
+
+  let newTab = await BrowserTestUtils.openNewForegroundTab(
+    browserWin.gBrowser,
+    TEST_PATH + "test_spammy_page.html"
+  );
+
+  await BrowserTestUtils.synthesizeMouseAtCenter(
+    "body",
+    {},
+    newTab.linkedBrowser
+  );
+
+  info("Waiting on all blocked downloads");
+  await gotAllBlockedDownloads;
+
+  let { downloadSpamProtection } = DownloadIntegration;
+  let spamList = downloadSpamProtection.getSpamListForWindow(browserWin);
+  is(
+    spamList._downloads[0].blockedDownloadsCount,
+    99,
+    "99 blocked downloads recorded"
+  );
+  ok(
+    spamList._downloads[0].error.becauseBlockedByReputationCheck,
+    "Download blocked because of reputation"
+  );
+  is(
+    spamList._downloads[0].error.reputationCheckVerdict,
+    "DownloadSpam",
+    "Verdict is DownloadSpam"
+  );
+
+  browserWin.focus();
+  await BrowserTestUtils.waitForPopupEvent(
+    browserWin.DownloadsPanel.panel,
+    "shown"
+  );
+
+  ok(browserWin.DownloadsPanel.isPanelShowing, "Download panel should open");
+  await Downloads.getList(Downloads.PUBLIC);
+
+  let listbox = browserWin.document.getElementById("downloadsListBox");
+  ok(listbox, "Download list box present");
+
+  await TestUtils.waitForCondition(() => {
+    return listbox.childElementCount == 2 && !listbox.getAttribute("disabled");
+  }, "2 downloads = 1 allowed download and 1 for 99 downloads blocked");
+
+  let spamElement = listbox.itemChildren[0].classList.contains(
+    "temporary-block"
+  )
+    ? listbox.itemChildren[0]
+    : listbox.itemChildren[1];
+
+  ok(spamElement.classList.contains("temporary-block"), "Download is blocked");
+
+  info("Testing spam protection in a second window");
+
+  browserWin.DownloadsPanel.hidePanel();
+  DownloadIntegration.downloadSpamProtection.removeDownloadSpamForWindow(
+    TEST_URI,
+    browserWin
+  );
+
+  ok(
+    !browserWin.DownloadsPanel.isPanelShowing,
+    "Download panel should be closed in first window"
+  );
+  is(
+    listbox.childElementCount,
+    1,
+    "First window's download list should have one item - the download that wasn't blocked"
+  );
+
+  let browserWin2 = await BrowserTestUtils.openNewBrowserWindow();
+  let observedBlockedDownloads2 = 0;
+  let gotAllBlockedDownloads2 = TestUtils.topicObserved(
+    "blocked-automatic-download",
+    () => {
+      return ++observedBlockedDownloads2 >= 100;
+    }
+  );
+
+  let newTab2 = await BrowserTestUtils.openNewForegroundTab(
+    browserWin2.gBrowser,
+    TEST_PATH + "test_spammy_page.html"
+  );
+  await BrowserTestUtils.synthesizeMouseAtCenter(
+    "body",
+    {},
+    newTab2.linkedBrowser
+  );
+
+  info("Waiting on all blocked downloads in second window");
+  await gotAllBlockedDownloads2;
+
+  let spamList2 = downloadSpamProtection.getSpamListForWindow(browserWin2);
+  is(
+    spamList2._downloads[0].blockedDownloadsCount,
+    100,
+    "100 blocked downloads recorded in second window"
+  );
+  ok(
+    !spamList._downloads[0]?.blockedDownloadsCount,
+    "No blocked downloads in first window"
+  );
+
+  browserWin2.focus();
+  await BrowserTestUtils.waitForPopupEvent(
+    browserWin2.DownloadsPanel.panel,
+    "shown"
+  );
+
+  ok(
+    browserWin2.DownloadsPanel.isPanelShowing,
+    "Download panel should open in second window"
+  );
+
+  ok(
+    !browserWin.DownloadsPanel.isPanelShowing,
+    "Download panel should not open in first window"
+  );
+
+  let listbox2 = browserWin2.document.getElementById("downloadsListBox");
+  ok(listbox2, "Download list box present");
+
+  await TestUtils.waitForCondition(() => {
+    return (
+      listbox2.childElementCount == 2 && !listbox2.getAttribute("disabled")
+    );
+  }, "2 downloads = 1 allowed download from first window, and 1 for 100 downloads blocked in second window");
+
+  is(
+    listbox.childElementCount,
+    1,
+    "First window's download list should still have one item - the download that wasn't blocked"
+  );
+
+  let spamElement2 = listbox2.itemChildren[0].classList.contains(
+    "temporary-block"
+  )
+    ? listbox2.itemChildren[0]
+    : listbox2.itemChildren[1];
+
+  ok(spamElement2.classList.contains("temporary-block"), "Download is blocked");
+});
diff --git a/browser/components/downloads/test/browser/browser_download_starts_in_tmp.js b/browser/components/downloads/test/browser/browser_download_starts_in_tmp.js
new file mode 100644
index 0000000000..2577a20157
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_download_starts_in_tmp.js
@@ -0,0 +1,264 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const UCT_URI = "chrome://mozapps/content/downloads/unknownContentType.xhtml";
+// Need to start the server before `httpUrl` works.
+startServer();
+const DOWNLOAD_URL = httpUrl("interruptible.txt");
+
+let gDownloadDir;
+
+let gExternalHelperAppService = Cc[
+  "@mozilla.org/uriloader/external-helper-app-service;1"
+].getService(Ci.nsIExternalHelperAppService);
+gExternalHelperAppService.QueryInterface(Ci.nsIObserver);
+
+add_setup(async function() {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["browser.download.start_downloads_in_tmp_dir", true],
+      ["browser.helperApps.deleteTempFileOnExit", true],
+    ],
+  });
+  registerCleanupFunction(task_resetState);
+  gDownloadDir = new FileUtils.File(await setDownloadDir());
+  registerCleanupFunction(() => {
+    Services.prefs.clearUserPref("browser.download.dir");
+    Services.prefs.clearUserPref("browser.download.folderList");
+  });
+});
+
+add_task(async function test_download_asking_starts_in_tmp() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["browser.download.always_ask_before_handling_new_types", true]],
+  });
+  let list = await Downloads.getList(Downloads.PUBLIC);
+  let downloadStarted = new Promise(resolve => {
+    let view = {
+      onDownloadAdded(download) {
+        list.removeView(view);
+        resolve(download);
+      },
+    };
+    list.addView(view);
+  });
+  // Wait for the download prompting dialog
+  let dialogPromise = BrowserTestUtils.domWindowOpenedAndLoaded(
+    null,
+    win => win.document.documentURI == UCT_URI
+  );
+  serveInterruptibleAsDownload();
+  mustInterruptResponses();
+  await BrowserTestUtils.withNewTab(
+    {
+      gBrowser,
+      url: DOWNLOAD_URL,
+      waitForLoad: false,
+      waitForStop: true,
+    },
+    async function() {
+      let dialogWin = await dialogPromise;
+      let tempFile = dialogWin.dialog.mLauncher.targetFile;
+      ok(
+        !tempFile.parent.equals(gDownloadDir),
+        "Should not have put temp file in the downloads dir."
+      );
+
+      let dialogEl = dialogWin.document.querySelector("dialog");
+      dialogEl.getButton("accept").disabled = false;
+      dialogEl.acceptDialog();
+      let download = await downloadStarted;
+      is(
+        PathUtils.parent(download.target.path),
+        gDownloadDir.path,
+        "Should have put final file in the downloads dir."
+      );
+      continueResponses();
+      await download.whenSucceeded();
+      await IOUtils.remove(download.target.path);
+    }
+  );
+  await list.removeFinished();
+});
+
+add_task(async function test_download_asking_and_opening_opens_from_tmp() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["browser.download.always_ask_before_handling_new_types", true]],
+  });
+  let list = await Downloads.getList(Downloads.PUBLIC);
+  let downloadStarted = new Promise(resolve => {
+    let view = {
+      onDownloadAdded(download) {
+        list.removeView(view);
+        resolve(download);
+      },
+    };
+    list.addView(view);
+  });
+  // Wait for the download prompting dialog
+  let dialogPromise = BrowserTestUtils.domWindowOpenedAndLoaded(
+    null,
+    win => win.document.documentURI == UCT_URI
+  );
+
+  let oldLaunchFile = DownloadIntegration.launchFile;
+  let promiseLaunchFileCalled = new Promise(resolve => {
+    DownloadIntegration.launchFile = file => {
+      ok(true, "The file should be launched with an external application");
+      resolve(file);
+      DownloadIntegration.launchFile = oldLaunchFile;
+    };
+  });
+  registerCleanupFunction(() => {
+    DownloadIntegration.launchFile = oldLaunchFile;
+  });
+
+  serveInterruptibleAsDownload();
+  mustInterruptResponses();
+  await BrowserTestUtils.withNewTab(
+    {
+      gBrowser,
+      url: DOWNLOAD_URL,
+      waitForLoad: false,
+      waitForStop: true,
+    },
+    async function() {
+      let dialogWin = await dialogPromise;
+      let tempFile = dialogWin.dialog.mLauncher.targetFile;
+      ok(
+        !tempFile.parent.equals(gDownloadDir),
+        "Should not have put temp file in the downloads dir."
+      );
+
+      dialogWin.document.getElementById("open").click();
+      let dialogEl = dialogWin.document.querySelector("dialog");
+      dialogEl.getButton("accept").disabled = false;
+      dialogEl.acceptDialog();
+      let download = await downloadStarted;
+      isnot(
+        PathUtils.parent(download.target.path),
+        gDownloadDir.path,
+        "Should not have put final file in the downloads dir when it's supposed to be automatically opened."
+      );
+      continueResponses();
+      await download.whenSucceeded();
+      await download.refresh();
+      isnot(
+        PathUtils.parent(download.target.path),
+        gDownloadDir.path,
+        "Once finished the download should not be in the downloads dir when it's supposed to be automatically opened."
+      );
+      let file = await promiseLaunchFileCalled;
+      ok(
+        !file.parent.equals(gDownloadDir),
+        "Should not have put opened file in the downloads dir."
+      );
+
+      // Pretend that we've quit so we wipe all the files:
+      gExternalHelperAppService.observe(null, "profile-before-change", "");
+      // Now the file should go away, but that's async...
+
+      let f = new FileUtils.File(download.target.path);
+      await TestUtils.waitForCondition(
+        () => !f.exists(),
+        "Temp file should be removed",
+        500
+      ).catch(err => ok(false, err));
+      ok(!f.exists(), "Temp file should be removed.");
+
+      await IOUtils.remove(download.target.path);
+    }
+  );
+  await list.removeFinished();
+});
+
+// Check that if we open the file automatically, it opens from the temp dir.
+add_task(async function test_download_automatically_opened_from_tmp() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["browser.download.always_ask_before_handling_new_types", false]],
+  });
+  serveInterruptibleAsDownload();
+  mustInterruptResponses();
+
+  let list = await Downloads.getList(Downloads.PUBLIC);
+  let downloadStarted = new Promise(resolve => {
+    let view = {
+      onDownloadAdded(download) {
+        list.removeView(view);
+        resolve(download);
+      },
+    };
+    list.addView(view);
+  });
+
+  const handlerSvc = Cc["@mozilla.org/uriloader/handler-service;1"].getService(
+    Ci.nsIHandlerService
+  );
+  const mimeSvc = Cc["@mozilla.org/mime;1"].getService(Ci.nsIMIMEService);
+
+  let txtHandlerInfo = mimeSvc.getFromTypeAndExtension("text/plain", "txt");
+  txtHandlerInfo.preferredAction = Ci.nsIHandlerInfo.useSystemDefault;
+  txtHandlerInfo.alwaysAskBeforeHandling = false;
+  handlerSvc.store(txtHandlerInfo);
+  registerCleanupFunction(() => handlerSvc.remove(txtHandlerInfo));
+
+  let oldLaunchFile = DownloadIntegration.launchFile;
+  let promiseLaunchFileCalled = new Promise(resolve => {
+    DownloadIntegration.launchFile = file => {
+      ok(true, "The file should be launched with an external application");
+      resolve(file);
+      DownloadIntegration.launchFile = oldLaunchFile;
+    };
+  });
+  registerCleanupFunction(() => {
+    DownloadIntegration.launchFile = oldLaunchFile;
+  });
+
+  await BrowserTestUtils.withNewTab(
+    {
+      gBrowser,
+      url: DOWNLOAD_URL,
+      waitForLoad: false,
+      waitForStop: true,
+    },
+    async function() {
+      let download = await downloadStarted;
+      isnot(
+        PathUtils.parent(download.target.partFilePath),
+        gDownloadDir.path,
+        "Should not start the download in the downloads dir."
+      );
+      continueResponses();
+      await download.whenSucceeded();
+      isnot(
+        PathUtils.parent(download.target.path),
+        gDownloadDir.path,
+        "Should not have put final file in the downloads dir."
+      );
+      let file = await promiseLaunchFileCalled;
+      ok(
+        !file.parent.equals(gDownloadDir),
+        "Should not have put opened file in the downloads dir."
+      );
+
+      // Pretend that we've quit so we wipe all the files:
+      gExternalHelperAppService.observe(null, "profile-before-change", "");
+      // Now the file should go away, but that's async...
+
+      let f = new FileUtils.File(download.target.path);
+      await TestUtils.waitForCondition(
+        () => !f.exists(),
+        "Temp file should be removed",
+        500
+      ).catch(err => ok(false, err));
+      ok(!f.exists(), "Temp file should be removed.");
+
+      await IOUtils.remove(download.target.path);
+    }
+  );
+
+  handlerSvc.remove(txtHandlerInfo);
+  await list.removeFinished();
+});
diff --git a/browser/components/downloads/test/browser/browser_downloads_autohide.js b/browser/components/downloads/test/browser/browser_downloads_autohide.js
new file mode 100644
index 0000000000..dbe7b95c13
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_downloads_autohide.js
@@ -0,0 +1,519 @@
+/* -*- indent-tabs-mode: nil; js-indent-level: 2 -*- */
+/* vim: set ts=2 et sw=2 tw=80: */
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const kDownloadAutoHidePref = "browser.download.autohideButton";
+
+registerCleanupFunction(async function() {
+  Services.prefs.clearUserPref(kDownloadAutoHidePref);
+  if (document.documentElement.hasAttribute("customizing")) {
+    await gCustomizeMode.reset();
+    await promiseCustomizeEnd();
+  } else {
+    CustomizableUI.reset();
+  }
+});
+
+add_setup(async () => {
+  // Disable window occlusion. See bug 1733955 / bug 1779559.
+  if (navigator.platform.indexOf("Win") == 0) {
+    await SpecialPowers.pushPrefEnv({
+      set: [["widget.windows.window_occlusion_tracking.enabled", false]],
+    });
+  }
+});
+
+add_task(async function checkStateDuringPrefFlips() {
+  ok(
+    Services.prefs.getBoolPref(kDownloadAutoHidePref),
+    "Should be autohiding the button by default"
+  );
+  ok(
+    !DownloadsIndicatorView.hasDownloads,
+    "Should be no downloads when starting the test"
+  );
+  let downloadsButton = document.getElementById("downloads-button");
+  ok(
+    downloadsButton.hasAttribute("hidden"),
+    "Button should be hidden in the toolbar"
+  );
+  await gCustomizeMode.addToPanel(downloadsButton);
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button shouldn't be hidden in the panel"
+  );
+  ok(
+    !Services.prefs.getBoolPref(kDownloadAutoHidePref),
+    "Pref got set to false when the user moved the button"
+  );
+  gCustomizeMode.addToToolbar(downloadsButton);
+  ok(
+    !Services.prefs.getBoolPref(kDownloadAutoHidePref),
+    "Pref remains false when the user moved the button"
+  );
+  Services.prefs.setBoolPref(kDownloadAutoHidePref, true);
+  ok(
+    downloadsButton.hasAttribute("hidden"),
+    "Button should be hidden again in the toolbar " +
+      "now that we flipped the pref"
+  );
+  Services.prefs.setBoolPref(kDownloadAutoHidePref, false);
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button shouldn't be hidden with autohide turned off"
+  );
+  await gCustomizeMode.addToPanel(downloadsButton);
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button shouldn't be hidden with autohide turned off " +
+      "after moving it to the panel"
+  );
+  gCustomizeMode.addToToolbar(downloadsButton);
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button shouldn't be hidden with autohide turned off " +
+      "after moving it back to the toolbar"
+  );
+  await gCustomizeMode.addToPanel(downloadsButton);
+  Services.prefs.setBoolPref(kDownloadAutoHidePref, true);
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button should still not be hidden with autohide turned back on " +
+      "because it's in the panel"
+  );
+  // Use CUI directly instead of the customize mode APIs,
+  // to avoid tripping the "automatically turn off autohide" code.
+  CustomizableUI.addWidgetToArea("downloads-button", "nav-bar");
+  ok(
+    downloadsButton.hasAttribute("hidden"),
+    "Button should be hidden again in the toolbar"
+  );
+  gCustomizeMode.removeFromArea(downloadsButton);
+  Services.prefs.setBoolPref(kDownloadAutoHidePref, false);
+  // Can't use gCustomizeMode.addToToolbar here because it doesn't work for
+  // palette items if the window isn't in customize mode:
+  CustomizableUI.addWidgetToArea(
+    downloadsButton.id,
+    CustomizableUI.AREA_NAVBAR
+  );
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button should be unhidden again in the toolbar " +
+      "even if the pref was flipped while the button was in the palette"
+  );
+  Services.prefs.setBoolPref(kDownloadAutoHidePref, true);
+});
+
+add_task(async function checkStateInCustomizeMode() {
+  ok(
+    Services.prefs.getBoolPref("browser.download.autohideButton"),
+    "Should be autohiding the button"
+  );
+  let downloadsButton = document.getElementById("downloads-button");
+  await promiseCustomizeStart();
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button should be shown in customize mode."
+  );
+  await promiseCustomizeEnd();
+  ok(
+    downloadsButton.hasAttribute("hidden"),
+    "Button should be hidden if it's in the toolbar " +
+      "after customize mode without any moves."
+  );
+  await promiseCustomizeStart();
+  await gCustomizeMode.addToPanel(downloadsButton);
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button should be shown in customize mode when moved to the panel"
+  );
+  gCustomizeMode.addToToolbar(downloadsButton);
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button should be shown in customize mode when moved back to the toolbar"
+  );
+  gCustomizeMode.removeFromArea(downloadsButton);
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button should be shown in customize mode when in the palette"
+  );
+  Services.prefs.setBoolPref(kDownloadAutoHidePref, false);
+  Services.prefs.setBoolPref(kDownloadAutoHidePref, true);
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button should be shown in customize mode " +
+      "even when flipping the autohide pref"
+  );
+  await gCustomizeMode.addToPanel(downloadsButton);
+  await promiseCustomizeEnd();
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button should be shown after customize mode when moved to the panel"
+  );
+  await promiseCustomizeStart();
+  gCustomizeMode.addToToolbar(downloadsButton);
+  await promiseCustomizeEnd();
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button should be shown in the toolbar after " +
+      "customize mode because we moved it."
+  );
+  await promiseCustomizeStart();
+  await gCustomizeMode.reset();
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button should be shown in the toolbar in customize mode after a reset."
+  );
+  await gCustomizeMode.undoReset();
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button should be shown in the toolbar in customize mode " +
+      "when undoing the reset."
+  );
+  await gCustomizeMode.addToPanel(downloadsButton);
+  await gCustomizeMode.reset();
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button should be shown in the toolbar in customize mode " +
+      "after a reset moved it."
+  );
+  await gCustomizeMode.undoReset();
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button should be shown in the panel in customize mode " +
+      "when undoing the reset."
+  );
+  await gCustomizeMode.reset();
+  await promiseCustomizeEnd();
+});
+
+add_task(async function checkStateInCustomizeModeMultipleWindows() {
+  ok(
+    Services.prefs.getBoolPref("browser.download.autohideButton"),
+    "Should be autohiding the button"
+  );
+  let downloadsButton = document.getElementById("downloads-button");
+  await promiseCustomizeStart();
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button should be shown in customize mode."
+  );
+  let otherWin = await BrowserTestUtils.openNewBrowserWindow();
+  let otherDownloadsButton = otherWin.document.getElementById(
+    "downloads-button"
+  );
+  ok(
+    otherDownloadsButton.hasAttribute("hidden"),
+    "Button should be hidden in the other window."
+  );
+
+  // Use CUI directly instead of the customize mode APIs,
+  // to avoid tripping the "automatically turn off autohide" code.
+  CustomizableUI.addWidgetToArea(
+    "downloads-button",
+    CustomizableUI.AREA_FIXED_OVERFLOW_PANEL
+  );
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button should still be shown in customize mode."
+  );
+  ok(
+    !otherDownloadsButton.hasAttribute("hidden"),
+    "Button should be shown in the other window too because it's in a panel."
+  );
+
+  CustomizableUI.addWidgetToArea(
+    "downloads-button",
+    CustomizableUI.AREA_NAVBAR
+  );
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button should still be shown in customize mode."
+  );
+  ok(
+    otherDownloadsButton.hasAttribute("hidden"),
+    "Button should be hidden again in the other window."
+  );
+
+  Services.prefs.setBoolPref(kDownloadAutoHidePref, false);
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button should be shown in customize mode"
+  );
+  ok(
+    !otherDownloadsButton.hasAttribute("hidden"),
+    "Button should be shown in the other window with the pref flipped"
+  );
+
+  Services.prefs.setBoolPref(kDownloadAutoHidePref, true);
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button should be shown in customize mode " +
+      "even when flipping the autohide pref"
+  );
+  ok(
+    otherDownloadsButton.hasAttribute("hidden"),
+    "Button should be hidden in the other window with the pref flipped again"
+  );
+
+  await gCustomizeMode.addToPanel(downloadsButton);
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button should still be shown in customize mode."
+  );
+  ok(
+    !otherDownloadsButton.hasAttribute("hidden"),
+    "Button should be shown in the other window too because it's in a panel."
+  );
+
+  gCustomizeMode.removeFromArea(downloadsButton);
+  ok(
+    !Services.prefs.getBoolPref(kDownloadAutoHidePref),
+    "Autohide pref turned off by moving the button"
+  );
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button should still be shown in customize mode."
+  );
+  // Don't need to assert in the other window - button is gone there.
+
+  await gCustomizeMode.reset();
+  ok(
+    Services.prefs.getBoolPref(kDownloadAutoHidePref),
+    "Autohide pref reset by reset()"
+  );
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button should still be shown in customize mode."
+  );
+  ok(
+    otherDownloadsButton.hasAttribute("hidden"),
+    "Button should be hidden in the other window."
+  );
+  ok(
+    otherDownloadsButton.closest("#nav-bar"),
+    "Button should be back in the nav bar in the other window."
+  );
+
+  await promiseCustomizeEnd();
+  ok(
+    downloadsButton.hasAttribute("hidden"),
+    "Button should be hidden again outside of customize mode"
+  );
+  await BrowserTestUtils.closeWindow(otherWin);
+});
+
+add_task(async function checkStateForDownloads() {
+  ok(
+    Services.prefs.getBoolPref("browser.download.autohideButton"),
+    "Should be autohiding the button"
+  );
+  let downloadsButton = document.getElementById("downloads-button");
+  ok(
+    downloadsButton.hasAttribute("hidden"),
+    "Button should be hidden when there are no downloads."
+  );
+
+  await task_addDownloads([{ state: DownloadsCommon.DOWNLOAD_DOWNLOADING }]);
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button should be unhidden when there are downloads."
+  );
+  let publicList = await Downloads.getList(Downloads.PUBLIC);
+  let downloads = await publicList.getAll();
+  for (let download of downloads) {
+    publicList.remove(download);
+  }
+  ok(
+    downloadsButton.hasAttribute("hidden"),
+    "Button should be hidden when the download is removed"
+  );
+  await task_addDownloads([{ state: DownloadsCommon.DOWNLOAD_DOWNLOADING }]);
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button should be unhidden when there are downloads."
+  );
+
+  Services.prefs.setBoolPref(kDownloadAutoHidePref, false);
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button should still be unhidden."
+  );
+
+  downloads = await publicList.getAll();
+  for (let download of downloads) {
+    publicList.remove(download);
+  }
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button should still be unhidden because the pref was flipped."
+  );
+  Services.prefs.setBoolPref(kDownloadAutoHidePref, true);
+  ok(
+    downloadsButton.hasAttribute("hidden"),
+    "Button should be hidden now that the pref flipped back " +
+      "because there were already no downloads."
+  );
+
+  gCustomizeMode.addToPanel(downloadsButton);
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button should not be hidden in the panel."
+  );
+
+  await task_addDownloads([{ state: DownloadsCommon.DOWNLOAD_DOWNLOADING }]);
+
+  downloads = await publicList.getAll();
+  for (let download of downloads) {
+    publicList.remove(download);
+  }
+
+  ok(
+    !downloadsButton.hasAttribute("hidden"),
+    "Button should still not be hidden in the panel " +
+      "when downloads count reaches 0 after being non-0."
+  );
+
+  CustomizableUI.reset();
+});
+
+/**
+ * Check that if the button is moved to the palette, we unhide it
+ * in customize mode even if it was always hidden. We use a new
+ * window to test this.
+ */
+add_task(async function checkStateWhenHiddenInPalette() {
+  ok(
+    Services.prefs.getBoolPref(kDownloadAutoHidePref),
+    "Pref should be causing us to autohide"
+  );
+  gCustomizeMode.removeFromArea(document.getElementById("downloads-button"));
+  // In a new window, the button will have been hidden
+  let otherWin = await BrowserTestUtils.openNewBrowserWindow();
+  ok(
+    !otherWin.document.getElementById("downloads-button"),
+    "Button shouldn't be visible in the window"
+  );
+
+  let paletteButton = otherWin.gNavToolbox.palette.querySelector(
+    "#downloads-button"
+  );
+  ok(paletteButton, "Button should exist in the palette");
+  if (paletteButton) {
+    ok(paletteButton.hidden, "Button will still have the hidden attribute");
+    await promiseCustomizeStart(otherWin);
+    ok(
+      !paletteButton.hidden,
+      "Button should no longer be hidden in customize mode"
+    );
+    ok(
+      otherWin.document.getElementById("downloads-button"),
+      "Button should be in the document now."
+    );
+    await promiseCustomizeEnd(otherWin);
+    // We purposefully don't assert anything about what happens next.
+    // It doesn't really matter if the button remains unhidden in
+    // the palette, and if we move it we'll unhide it then (the other
+    // tests check this).
+  }
+  await BrowserTestUtils.closeWindow(otherWin);
+  CustomizableUI.reset();
+});
+
+add_task(async function checkContextMenu() {
+  let contextMenu = document.getElementById("toolbar-context-menu");
+  let checkbox = document.getElementById(
+    "toolbar-context-autohide-downloads-button"
+  );
+  let button = document.getElementById("downloads-button");
+
+  is(
+    Services.prefs.getBoolPref(kDownloadAutoHidePref),
+    true,
+    "Pref should be causing us to autohide"
+  );
+  is(
+    DownloadsIndicatorView.hasDownloads,
+    false,
+    "Should be no downloads when starting the test"
+  );
+  is(button.hidden, true, "Downloads button is hidden");
+
+  info("Simulate a download to show the downloads button.");
+  DownloadsIndicatorView.hasDownloads = true;
+  is(button.hidden, false, "Downloads button is visible");
+
+  info("Check context menu");
+  await openContextMenu(button);
+  is(checkbox.hidden, false, "Auto-hide checkbox is visible");
+  is(checkbox.getAttribute("checked"), "true", "Auto-hide is enabled");
+
+  info("Disable auto-hide via context menu");
+  clickCheckbox(checkbox);
+  is(
+    Services.prefs.getBoolPref(kDownloadAutoHidePref),
+    false,
+    "Pref has been set to false"
+  );
+
+  info("Clear downloads");
+  DownloadsIndicatorView.hasDownloads = false;
+  is(button.hidden, false, "Downloads button is still visible");
+
+  info("Check context menu");
+  await openContextMenu(button);
+  is(checkbox.hidden, false, "Auto-hide checkbox is visible");
+  is(checkbox.hasAttribute("checked"), false, "Auto-hide is disabled");
+
+  info("Enable auto-hide via context menu");
+  clickCheckbox(checkbox);
+  is(button.hidden, true, "Downloads button is hidden");
+  is(
+    Services.prefs.getBoolPref(kDownloadAutoHidePref),
+    true,
+    "Pref has been set to true"
+  );
+
+  info("Check context menu in another button");
+  await openContextMenu(document.getElementById("reload-button"));
+  is(checkbox.hidden, true, "Auto-hide checkbox is hidden");
+  contextMenu.hidePopup();
+
+  info("Open popup directly");
+  contextMenu.openPopup();
+  is(checkbox.hidden, true, "Auto-hide checkbox is hidden");
+  contextMenu.hidePopup();
+});
+
+function promiseCustomizeStart(aWindow = window) {
+  return new Promise(resolve => {
+    aWindow.gNavToolbox.addEventListener("customizationready", resolve, {
+      once: true,
+    });
+    aWindow.gCustomizeMode.enter();
+  });
+}
+
+function promiseCustomizeEnd(aWindow = window) {
+  return new Promise(resolve => {
+    aWindow.gNavToolbox.addEventListener("aftercustomization", resolve, {
+      once: true,
+    });
+    aWindow.gCustomizeMode.exit();
+  });
+}
+
+function clickCheckbox(checkbox) {
+  // Clicking a checkbox toggles its checkedness first.
+  if (checkbox.getAttribute("checked") == "true") {
+    checkbox.removeAttribute("checked");
+  } else {
+    checkbox.setAttribute("checked", "true");
+  }
+  // Then it runs the command and closes the popup.
+  checkbox.doCommand();
+  checkbox.parentElement.hidePopup();
+}
diff --git a/browser/components/downloads/test/browser/browser_downloads_context_menu_always_open_similar_files.js b/browser/components/downloads/test/browser/browser_downloads_context_menu_always_open_similar_files.js
new file mode 100644
index 0000000000..2113aed7ff
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_downloads_context_menu_always_open_similar_files.js
@@ -0,0 +1,243 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+let gMimeSvc = Cc["@mozilla.org/mime;1"].getService(Ci.nsIMIMEService);
+let gHandlerSvc = Cc["@mozilla.org/uriloader/handler-service;1"].getService(
+  Ci.nsIHandlerService
+);
+
+let gDownloadDir;
+const TestFiles = {};
+let downloads = [];
+const {
+  handleInternally,
+  saveToDisk,
+  useSystemDefault,
+  alwaysAsk,
+} = Ci.nsIHandlerInfo;
+
+function ensureMIMEState({ preferredAction, alwaysAskBeforeHandling = false }) {
+  const mimeInfo = gMimeSvc.getFromTypeAndExtension("text/plain", "txt");
+  mimeInfo.preferredAction = preferredAction;
+  mimeInfo.alwaysAskBeforeHandling = alwaysAskBeforeHandling;
+  gHandlerSvc.store(mimeInfo);
+}
+
+async function createDownloadFile() {
+  if (!gDownloadDir) {
+    gDownloadDir = await setDownloadDir();
+  }
+  info("Created download directory: " + gDownloadDir);
+  TestFiles.txt = await createDownloadedFile(
+    PathUtils.join(gDownloadDir, "downloaded.txt"),
+    "Test file"
+  );
+  info("Created downloaded text file at:" + TestFiles.txt.path);
+
+  info("Setting path for download file");
+  // Set target for download file. Otherwise, file will default to .file instead of txt
+  // when we prepare our downloads - particularly in task_addDownloads().
+  let targetPath = PathUtils.join(PathUtils.tempDir, "downloaded.txt");
+  let target = new FileUtils.File(targetPath);
+  target.createUnique(Ci.nsIFile.NORMAL_FILE_TYPE, FileUtils.PERMS_FILE);
+  downloads.push({
+    state: DownloadsCommon.DOWNLOAD_FINISHED,
+    contentType: "text/plain",
+    target,
+  });
+}
+
+async function prepareDownloadFiles(downloadList) {
+  // prepare downloads
+  await task_addDownloads(downloads);
+  let [download] = await downloadList.getAll();
+  info("Download succeeded? " + download.succeeded);
+  info("Download target exists? " + download.target.exists);
+}
+
+add_setup(async function() {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["browser.download.improvements_to_download_panel", true],
+      ["browser.download.always_ask_before_handling_new_types", false],
+    ],
+  });
+  const originalOpenDownload = DownloadsCommon.openDownload;
+  // overwrite DownloadsCommon.openDownload to prevent file from opening during tests
+  DownloadsCommon.openDownload = async () => {
+    info("Overwriting openDownload for tests");
+  };
+
+  registerCleanupFunction(async () => {
+    DownloadsCommon.openDownload = originalOpenDownload;
+    info("Resetting downloads and closing downloads panel");
+    await task_resetState();
+  });
+
+  // remove download files, empty out collections
+  let downloadList = await Downloads.getList(Downloads.ALL);
+  let downloadCount = (await downloadList.getAll()).length;
+  is(downloadCount, 0, "At the start of the test, there should be 0 downloads");
+
+  await createDownloadFile();
+  await prepareDownloadFiles(downloadList);
+});
+
+add_task(async function test_checkbox_useSystemDefault() {
+  // force mimetype pref
+  ensureMIMEState({ preferredAction: useSystemDefault });
+
+  await task_openPanel();
+  await TestUtils.waitForCondition(() => {
+    let downloadsListBox = document.getElementById("downloadsListBox");
+    downloadsListBox.removeAttribute("disabled");
+    return downloadsListBox.childElementCount == downloads.length;
+  });
+
+  info("trigger the context menu");
+  let itemTarget = document.querySelector(
+    "#downloadsListBox richlistitem .downloadMainArea"
+  );
+
+  let contextMenu = await openContextMenu(itemTarget);
+  let alwaysOpenSimilarFilesItem = contextMenu.querySelector(
+    ".downloadAlwaysOpenSimilarFilesMenuItem"
+  );
+
+  ok(
+    !BrowserTestUtils.is_hidden(alwaysOpenSimilarFilesItem),
+    "alwaysOpenSimilarFiles should be visible"
+  );
+  ok(
+    alwaysOpenSimilarFilesItem.hasAttribute("checked"),
+    "alwaysOpenSimilarFiles should have checkbox attribute"
+  );
+
+  contextMenu.hidePopup();
+  let hiddenPromise = BrowserTestUtils.waitForEvent(
+    DownloadsPanel.panel,
+    "popuphidden"
+  );
+  DownloadsPanel.hidePanel();
+  await hiddenPromise;
+});
+
+add_task(async function test_checkbox_saveToDisk() {
+  // force mimetype pref
+  ensureMIMEState({ preferredAction: saveToDisk });
+
+  await task_openPanel();
+  await TestUtils.waitForCondition(() => {
+    let downloadsListBox = document.getElementById("downloadsListBox");
+    downloadsListBox.removeAttribute("disabled");
+    return downloadsListBox.childElementCount == downloads.length;
+  });
+
+  info("trigger the context menu");
+  let itemTarget = document.querySelector(
+    "#downloadsListBox richlistitem .downloadMainArea"
+  );
+
+  let contextMenu = await openContextMenu(itemTarget);
+  let alwaysOpenSimilarFilesItem = contextMenu.querySelector(
+    ".downloadAlwaysOpenSimilarFilesMenuItem"
+  );
+
+  ok(
+    !BrowserTestUtils.is_hidden(alwaysOpenSimilarFilesItem),
+    "alwaysOpenSimilarFiles should be visible"
+  );
+  ok(
+    !alwaysOpenSimilarFilesItem.hasAttribute("checked"),
+    "alwaysOpenSimilarFiles should not have checkbox attribute"
+  );
+
+  contextMenu.hidePopup();
+  let hiddenPromise = BrowserTestUtils.waitForEvent(
+    DownloadsPanel.panel,
+    "popuphidden"
+  );
+  DownloadsPanel.hidePanel();
+  await hiddenPromise;
+});
+
+add_task(async function test_preferences_enable_alwaysOpenSimilarFiles() {
+  // Force mimetype pref
+  ensureMIMEState({ preferredAction: saveToDisk });
+
+  // open panel
+  await task_openPanel();
+  await TestUtils.waitForCondition(() => {
+    let downloadsListBox = document.getElementById("downloadsListBox");
+    downloadsListBox.removeAttribute("disabled");
+    return downloadsListBox.childElementCount == downloads.length;
+  });
+
+  info("trigger the context menu");
+  let itemTarget = document.querySelector(
+    "#downloadsListBox richlistitem .downloadMainArea"
+  );
+
+  let contextMenu = await openContextMenu(itemTarget);
+  let alwaysOpenSimilarFilesItem = contextMenu.querySelector(
+    ".downloadAlwaysOpenSimilarFilesMenuItem"
+  );
+
+  alwaysOpenSimilarFilesItem.click();
+
+  await TestUtils.waitForCondition(() => {
+    let mimeInfo = gMimeSvc.getFromTypeAndExtension("text/plain", "txt");
+    return mimeInfo.preferredAction === useSystemDefault;
+  });
+  let mimeInfo = gMimeSvc.getFromTypeAndExtension("text/plain", "txt");
+
+  is(
+    mimeInfo.preferredAction,
+    useSystemDefault,
+    "Preference should switch to useSystemDefault"
+  );
+
+  contextMenu.hidePopup();
+  DownloadsPanel.hidePanel();
+});
+
+add_task(async function test_preferences_disable_alwaysOpenSimilarFiles() {
+  // Force mimetype pref
+  ensureMIMEState({ preferredAction: useSystemDefault });
+
+  await task_openPanel();
+  await TestUtils.waitForCondition(() => {
+    let downloadsListBox = document.getElementById("downloadsListBox");
+    downloadsListBox.removeAttribute("disabled");
+    return downloadsListBox.childElementCount == downloads.length;
+  });
+
+  info("trigger the context menu");
+  let itemTarget = document.querySelector(
+    "#downloadsListBox richlistitem .downloadMainArea"
+  );
+
+  let contextMenu = await openContextMenu(itemTarget);
+  let alwaysOpenSimilarFilesItem = contextMenu.querySelector(
+    ".downloadAlwaysOpenSimilarFilesMenuItem"
+  );
+
+  alwaysOpenSimilarFilesItem.click();
+
+  await TestUtils.waitForCondition(() => {
+    let mimeInfo = gMimeSvc.getFromTypeAndExtension("text/plain", "txt");
+    return mimeInfo.preferredAction === saveToDisk;
+  });
+  let mimeInfo = gMimeSvc.getFromTypeAndExtension("text/plain", "txt");
+
+  is(
+    mimeInfo.preferredAction,
+    saveToDisk,
+    "Preference should switch to saveToDisk"
+  );
+
+  contextMenu.hidePopup();
+  DownloadsPanel.hidePanel();
+});
diff --git a/browser/components/downloads/test/browser/browser_downloads_context_menu_delete_file.js b/browser/components/downloads/test/browser/browser_downloads_context_menu_delete_file.js
new file mode 100644
index 0000000000..7611b7e1c4
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_downloads_context_menu_delete_file.js
@@ -0,0 +1,254 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+var { DownloadHistory } = ChromeUtils.importESModule(
+  "resource://gre/modules/DownloadHistory.sys.mjs"
+);
+let gDownloadDir;
+let downloads = [];
+
+async function createDownloadFiles() {
+  if (!gDownloadDir) {
+    gDownloadDir = await setDownloadDir();
+  }
+  info("Created download directory: " + gDownloadDir);
+  info("Setting path for download file");
+  downloads.push({
+    state: DownloadsCommon.DOWNLOAD_FINISHED,
+    contentType: "text/plain",
+    target: await createDownloadedFile(
+      PathUtils.join(gDownloadDir, "downloaded.txt"),
+      "Test file"
+    ),
+  });
+  downloads.push({
+    state: DownloadsCommon.DOWNLOAD_FINISHED,
+    contentType: "text/javascript",
+    target: await createDownloadedFile(
+      PathUtils.join(gDownloadDir, "downloaded.js"),
+      "Test file"
+    ),
+  });
+}
+
+add_setup(startServer);
+
+registerCleanupFunction(async function() {
+  await task_resetState();
+  await PlacesUtils.history.clear();
+});
+
+add_task(async function test_download_deleteFile() {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["browser.download.improvements_to_download_panel", true],
+      ["browser.download.always_ask_before_handling_new_types", false],
+      ["browser.download.alwaysOpenPanel", false],
+      ["browser.download.clearHistoryOnDelete", 2],
+    ],
+  });
+
+  // remove download files, empty out collections
+  let downloadList = await Downloads.getList(Downloads.ALL);
+  let downloadCount = (await downloadList.getAll()).length;
+  is(downloadCount, 0, "At the start of the test, there should be 0 downloads");
+  await task_resetState();
+  await createDownloadFiles();
+  await task_addDownloads(downloads);
+  await task_openPanel();
+  await TestUtils.waitForCondition(() => {
+    let downloadsListBox = document.getElementById("downloadsListBox");
+    downloadsListBox.removeAttribute("disabled");
+    return downloadsListBox.childElementCount == downloads.length;
+  });
+
+  info("trigger the context menu");
+  let itemTarget = document.querySelector(
+    "#downloadsListBox richlistitem .downloadMainArea"
+  );
+  let contextMenu = await openContextMenu(itemTarget);
+  let deleteFileItem = contextMenu.querySelector(
+    '[command="downloadsCmd_deleteFile"]'
+  );
+  ok(
+    !BrowserTestUtils.is_hidden(deleteFileItem),
+    "deleteFileItem should be visible"
+  );
+
+  let target1 = downloads[1].target;
+  ok(target1.exists(), "downloaded.txt should exist");
+  info(`file path: ${target1.path}`);
+  let hiddenPromise = BrowserTestUtils.waitForEvent(
+    DownloadsPanel.panel,
+    "popuphidden"
+  );
+
+  contextMenu.activateItem(deleteFileItem);
+
+  await TestUtils.waitForCondition(() => !target1.exists());
+
+  await TestUtils.waitForCondition(() => {
+    let downloadsListBox = document.getElementById("downloadsListBox");
+    downloadsListBox.removeAttribute("disabled");
+    return downloadsListBox.childElementCount == 1;
+  });
+
+  await SpecialPowers.pushPrefEnv({
+    set: [["browser.download.clearHistoryOnDelete", 0]],
+  });
+  info("trigger the context menu again");
+  let itemTarget2 = document.querySelector(
+    "#downloadsListBox richlistitem .downloadMainArea"
+  );
+  let contextMenu2 = await openContextMenu(itemTarget2);
+  ok(
+    !BrowserTestUtils.is_hidden(deleteFileItem),
+    "deleteFileItem should be visible"
+  );
+  let target2 = downloads[0].target;
+  ok(target2.exists(), "downloaded.js should exist");
+  info(`file path: ${target2.path}`);
+  contextMenu2.activateItem(deleteFileItem);
+  await TestUtils.waitForCondition(() => !target2.exists());
+
+  let downloadsListBox = document.getElementById("downloadsListBox");
+  downloadsListBox.removeAttribute("disabled");
+  Assert.greater(
+    downloadsListBox.childElementCount,
+    0,
+    "There should be a download in the list"
+  );
+
+  ok(
+    !DownloadsView.richListBox.selectedItem._shell.isCommandEnabled(
+      "downloadsCmd_deleteFile"
+    ),
+    "Delete file command should be disabled"
+  );
+
+  DownloadsPanel.hidePanel();
+  await hiddenPromise;
+});
+
+add_task(async function test_about_downloads_deleteFile_for_history_download() {
+  await task_resetState();
+  await PlacesUtils.history.clear();
+
+  if (!gDownloadDir) {
+    gDownloadDir = await setDownloadDir();
+  }
+
+  let targetFile = await createDownloadedFile(
+    PathUtils.join(gDownloadDir, "test-download.txt"),
+    "blah blah blah"
+  );
+  let endTime;
+  try {
+    endTime = targetFile.creationTime;
+  } catch (e) {
+    endTime = Date.now();
+  }
+  let download = {
+    source: {
+      url: httpUrl(targetFile.leafName),
+      isPrivate: false,
+    },
+    target: {
+      path: targetFile.path,
+      size: targetFile.fileSize,
+    },
+    succeeded: true,
+    stopped: true,
+    endTime,
+    fileSize: targetFile.fileSize,
+    state: 1,
+  };
+
+  function promiseWaitForVisit(aUrl) {
+    return new Promise(resolve => {
+      function listener(aEvents) {
+        Assert.equal(aEvents.length, 1);
+        let event = aEvents[0];
+        Assert.equal(event.type, "page-visited");
+        if (event.url == aUrl) {
+          PlacesObservers.removeListener(["page-visited"], listener);
+          resolve([
+            event.visitTime,
+            event.transitionType,
+            event.lastKnownTitle,
+          ]);
+        }
+      }
+      PlacesObservers.addListener(["page-visited"], listener);
+    });
+  }
+
+  function waitForAnnotation(sourceUriSpec, annotationName) {
+    return TestUtils.waitForCondition(async () => {
+      let pageInfo = await PlacesUtils.history.fetch(sourceUriSpec, {
+        includeAnnotations: true,
+      });
+      return pageInfo && pageInfo.annotations.has(annotationName);
+    }, `Should have found annotation ${annotationName} for ${sourceUriSpec}.`);
+  }
+
+  // Add the download to history using the XPCOM service, then use the
+  // DownloadHistory module to save the associated metadata.
+  let promiseFileAnnotation = waitForAnnotation(
+    download.source.url,
+    "downloads/destinationFileURI"
+  );
+  let promiseMetaAnnotation = waitForAnnotation(
+    download.source.url,
+    "downloads/metaData"
+  );
+  let promiseVisit = promiseWaitForVisit(download.source.url);
+  await DownloadHistory.addDownloadToHistory(download);
+  await promiseVisit;
+  await DownloadHistory.updateMetaData(download);
+  await Promise.all([promiseFileAnnotation, promiseMetaAnnotation]);
+
+  let win = await openLibrary("Downloads");
+  registerCleanupFunction(function() {
+    win?.close();
+  });
+
+  let box = win.document.getElementById("downloadsListBox");
+  ok(box, "Should have list of downloads");
+  is(box.children.length, 1, "Should have 1 download.");
+  let kid = box.firstChild;
+  let desc = kid.querySelector(".downloadTarget");
+  let dl = kid._shell.download;
+  // This would just be an `is` check, but stray temp files
+  // if this test (or another in this dir) ever fails could throw that off.
+  ok(
+    desc.value.includes("test-download"),
+    `Label '${desc.value}' should include 'test-download'`
+  );
+  ok(kid.selected, "First item should be selected.");
+  ok(dl.placesNode, "Download should have history.");
+  ok(targetFile.exists(), "Download target should exist.");
+  let contextMenu = win.document.getElementById("downloadsContextMenu");
+  let popupShownPromise = BrowserTestUtils.waitForEvent(
+    contextMenu,
+    "popupshown"
+  );
+  EventUtils.synthesizeMouseAtCenter(
+    kid,
+    { type: "contextmenu", button: 2 },
+    win
+  );
+  await popupShownPromise;
+  let popupHiddenPromise = BrowserTestUtils.waitForEvent(
+    contextMenu,
+    "popuphidden"
+  );
+  contextMenu.activateItem(
+    contextMenu.querySelector(".downloadDeleteFileMenuItem")
+  );
+  await popupHiddenPromise;
+  await TestUtils.waitForCondition(() => !targetFile.exists());
+  info("History download target deleted.");
+});
diff --git a/browser/components/downloads/test/browser/browser_downloads_keynav.js b/browser/components/downloads/test/browser/browser_downloads_keynav.js
new file mode 100644
index 0000000000..4f23c737d4
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_downloads_keynav.js
@@ -0,0 +1,255 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+registerCleanupFunction(async function() {
+  await task_resetState();
+});
+
+function changeSelection(listbox, down) {
+  let selectPromise = BrowserTestUtils.waitForEvent(listbox, "select");
+  EventUtils.synthesizeKey(down ? "VK_DOWN" : "VK_UP", {});
+  return selectPromise;
+}
+
+add_task(async function test_downloads_keynav() {
+  // Ensure that state is reset in case previous tests didn't finish.
+  await task_resetState();
+
+  await SpecialPowers.pushPrefEnv({ set: [["accessibility.tabfocus", 7]] });
+
+  // Move the mouse pointer out of the way first so it doesn't
+  // interfere with the selection.
+  let listbox = document.getElementById("downloadsListBox");
+  EventUtils.synthesizeMouse(listbox, -5, -5, { type: "mousemove" });
+
+  let downloads = [];
+  for (let i = 0; i < 2; i++) {
+    downloads.push({ state: DownloadsCommon.DOWNLOAD_FINISHED });
+  }
+  downloads.push({ state: DownloadsCommon.DOWNLOAD_FAILED });
+  downloads.push({ state: DownloadsCommon.DOWNLOAD_BLOCKED });
+
+  await task_addDownloads(downloads);
+  await task_openPanel();
+
+  is(document.activeElement, listbox, "downloads list is focused");
+  is(listbox.selectedIndex, 0, "downloads list selected index starts at 0");
+
+  let footer = document.getElementById("downloadsHistory");
+
+  await changeSelection(listbox, true);
+  is(
+    document.activeElement,
+    listbox,
+    "downloads list is focused after down to index 1"
+  );
+  is(
+    listbox.selectedIndex,
+    1,
+    "downloads list selected index after down is pressed"
+  );
+
+  checkTabbing(listbox, 1);
+
+  await changeSelection(listbox, true);
+  is(
+    document.activeElement,
+    listbox,
+    "downloads list is focused after down to index 2"
+  );
+  is(
+    listbox.selectedIndex,
+    2,
+    "downloads list selected index after down to index 2"
+  );
+
+  checkTabbing(listbox, 2);
+
+  await changeSelection(listbox, true);
+  is(
+    document.activeElement,
+    listbox,
+    "downloads list is focused after down to index 3"
+  );
+  is(
+    listbox.selectedIndex,
+    3,
+    "downloads list selected index after down to index 3"
+  );
+
+  checkTabbing(listbox, 3);
+
+  await changeSelection(listbox, true);
+  is(document.activeElement, footer, "footer is focused");
+  is(
+    listbox.selectedIndex,
+    -1,
+    "downloads list selected index after down to footer"
+  );
+
+  EventUtils.synthesizeKey("VK_TAB", {});
+  is(
+    document.activeElement,
+    listbox,
+    "downloads list should be focused after tab when footer is focused"
+  );
+  is(
+    listbox.selectedIndex,
+    0,
+    "downloads list should be focused after tab when footer is focused selected index"
+  );
+
+  // Move back to the footer.
+  EventUtils.synthesizeKey("VK_TAB", { shiftKey: true });
+  is(document.activeElement, footer, "downloads footer is focused again");
+  is(
+    listbox.selectedIndex,
+    0,
+    "downloads footer is focused again selected index"
+  );
+
+  EventUtils.synthesizeKey("VK_DOWN", {});
+  is(
+    document.activeElement,
+    footer,
+    "downloads footer is still focused after down past footer"
+  );
+  is(
+    listbox.selectedIndex,
+    -1,
+    "downloads footer is still focused selected index after down past footer"
+  );
+
+  await changeSelection(listbox, false);
+  is(
+    document.activeElement,
+    listbox,
+    "downloads list is focused after up to index 3"
+  );
+  is(
+    listbox.selectedIndex,
+    3,
+    "downloads list selected index after up to index 3"
+  );
+
+  await changeSelection(listbox, false);
+  is(
+    document.activeElement,
+    listbox,
+    "downloads list is focused after up to index 2"
+  );
+  is(
+    listbox.selectedIndex,
+    2,
+    "downloads list selected index after up to index 2"
+  );
+
+  EventUtils.synthesizeMouseAtCenter(listbox.getItemAtIndex(0), {
+    type: "mousemove",
+  });
+  EventUtils.synthesizeMouseAtCenter(listbox.getItemAtIndex(1), {
+    type: "mousemove",
+  });
+  is(listbox.selectedIndex, 0, "downloads list selected index after mousemove");
+
+  checkTabbing(listbox, 0);
+
+  EventUtils.synthesizeKey("VK_UP", {});
+  is(
+    document.activeElement,
+    listbox,
+    "downloads list is still focused after up past start"
+  );
+  is(
+    listbox.selectedIndex,
+    0,
+    "downloads list is still focused after up past start selected index"
+  );
+
+  // Move the mouse pointer out of the way again so we don't
+  // hover over an item unintentionally if this test is run in verify mode.
+  EventUtils.synthesizeMouse(listbox, -5, -5, { type: "mousemove" });
+
+  await task_resetState();
+});
+
+async function checkTabbing(listbox, buttonIndex) {
+  let button = listbox.getItemAtIndex(buttonIndex).querySelector("button");
+  let footer = document.getElementById("downloadsHistory");
+
+  listbox.clientWidth; // flush layout first
+
+  EventUtils.synthesizeKey("VK_TAB", {});
+  is(
+    document.activeElement,
+    button,
+    "downloads button is focused after tab is pressed"
+  );
+  is(
+    listbox.selectedIndex,
+    buttonIndex,
+    "downloads button selected index after tab is pressed"
+  );
+
+  EventUtils.synthesizeKey("VK_TAB", {});
+  is(
+    document.activeElement,
+    footer,
+    "downloads footer is focused after tab is pressed again"
+  );
+  is(
+    listbox.selectedIndex,
+    buttonIndex,
+    "downloads footer selected index after tab is pressed again"
+  );
+
+  EventUtils.synthesizeKey("VK_TAB", {});
+  is(
+    document.activeElement,
+    listbox,
+    "downloads list is focused after tab is pressed yet again"
+  );
+  is(
+    listbox.selectedIndex,
+    buttonIndex,
+    "downloads list selected index after tab is pressed yet again"
+  );
+
+  EventUtils.synthesizeKey("VK_TAB", { shiftKey: true });
+  is(
+    document.activeElement,
+    footer,
+    "downloads footer is focused after shift+tab is pressed"
+  );
+  is(
+    listbox.selectedIndex,
+    buttonIndex,
+    "downloads footer selected index after shift+tab is pressed"
+  );
+
+  EventUtils.synthesizeKey("VK_TAB", { shiftKey: true });
+  is(
+    document.activeElement,
+    button,
+    "downloads button is focused after shift+tab is pressed again"
+  );
+  is(
+    listbox.selectedIndex,
+    buttonIndex,
+    "downloads button selected index after shift+tab is pressed again"
+  );
+
+  EventUtils.synthesizeKey("VK_TAB", { shiftKey: true });
+  is(
+    document.activeElement,
+    listbox,
+    "downloads list is focused after shift+tab is pressed yet again"
+  );
+  is(
+    listbox.selectedIndex,
+    buttonIndex,
+    "downloads list selected index after shift+tab is pressed yet again"
+  );
+}
diff --git a/browser/components/downloads/test/browser/browser_downloads_panel_block.js b/browser/components/downloads/test/browser/browser_downloads_panel_block.js
new file mode 100644
index 0000000000..d1791a5862
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_downloads_panel_block.js
@@ -0,0 +1,185 @@
+/* Any copyright is dedicated to the Public Domain.
+ * https://creativecommons.org/publicdomain/zero/1.0/ */
+
+/* eslint-disable mozilla/no-arbitrary-setTimeout */
+"use strict";
+
+add_task(async function mainTest() {
+  await task_resetState();
+
+  let verdicts = [
+    Downloads.Error.BLOCK_VERDICT_UNCOMMON,
+    Downloads.Error.BLOCK_VERDICT_MALWARE,
+    Downloads.Error.BLOCK_VERDICT_POTENTIALLY_UNWANTED,
+    Downloads.Error.BLOCK_VERDICT_INSECURE,
+  ];
+  await task_addDownloads(verdicts.map(v => makeDownload(v)));
+
+  // Check that the richlistitem for each download is correct.
+  for (let i = 0; i < verdicts.length; i++) {
+    await openPanel();
+
+    // Handle items backwards, using lastElementChild, to ensure there's no
+    // code wrongly resetting the selection to the first item during the process.
+    let item = DownloadsView.richListBox.lastElementChild;
+
+    info("Open the panel and click the item to show the subview.");
+    let viewPromise = promiseViewShown(DownloadsBlockedSubview.subview);
+    EventUtils.synthesizeMouseAtCenter(item, {});
+    await viewPromise;
+
+    // Items are listed in newest-to-oldest order, so e.g. the first item's
+    // verdict is the last element in the verdicts array.
+    Assert.ok(
+      DownloadsBlockedSubview.subview.getAttribute("verdict"),
+      verdicts[verdicts.count - i - 1]
+    );
+
+    info("Go back to the main view.");
+    viewPromise = promiseViewShown(DownloadsBlockedSubview.mainView);
+    DownloadsBlockedSubview.panelMultiView.goBack();
+    await viewPromise;
+
+    info("Show the subview again.");
+    viewPromise = promiseViewShown(DownloadsBlockedSubview.subview);
+    EventUtils.synthesizeMouseAtCenter(item, {});
+    await viewPromise;
+
+    info("Click the Open button.");
+    // The download should be unblocked and then opened,
+    // i.e., unblockAndOpenDownload() should be called on the item.  The panel
+    // should also be closed as a result, so wait for that too.
+    let unblockPromise = promiseUnblockAndSaveCalled(item);
+    let hidePromise = promisePanelHidden();
+    // Simulate a mousemove to ensure it's not wrongly being handled by the
+    // panel as the user changing download selection.
+    EventUtils.synthesizeMouseAtCenter(
+      DownloadsBlockedSubview.elements.unblockButton,
+      { type: "mousemove" }
+    );
+    EventUtils.synthesizeMouseAtCenter(
+      DownloadsBlockedSubview.elements.unblockButton,
+      {}
+    );
+    info("waiting for unblockOpen");
+    await unblockPromise;
+    info("waiting for hide panel");
+    await hidePromise;
+
+    window.focus();
+    await SimpleTest.promiseFocus(window);
+
+    info("Reopen the panel and show the subview again.");
+    await openPanel();
+    viewPromise = promiseViewShown(DownloadsBlockedSubview.subview);
+    EventUtils.synthesizeMouseAtCenter(item, {});
+    await viewPromise;
+
+    info("Click the Remove button.");
+    // The panel should close and the item should be removed from it.
+    hidePromise = promisePanelHidden();
+    EventUtils.synthesizeMouseAtCenter(
+      DownloadsBlockedSubview.elements.deleteButton,
+      {}
+    );
+    info("Waiting for hide panel");
+    await hidePromise;
+
+    info("Open the panel again and check the item is gone.");
+    await openPanel();
+    Assert.ok(!item.parentNode);
+
+    hidePromise = promisePanelHidden();
+    DownloadsPanel.hidePanel();
+    await hidePromise;
+  }
+
+  await task_resetState();
+});
+
+async function openPanel() {
+  // This function is insane but something intermittently causes the panel to be
+  // closed as soon as it's opening on Linux ASAN.  Maybe it would also happen
+  // on other build machines if the test ran often enough.  Not only is the
+  // panel closed, it's closed while it's opening, leaving DownloadsPanel._state
+  // such that when you try to open the panel again, it thinks it's already
+  // open, but it's not.  The result is that the test times out.
+  //
+  // What this does is call DownloadsPanel.showPanel over and over again until
+  // the panel is really open.  There are a few wrinkles:
+  //
+  // (1) When panel.state is "open", check four more times (for a total of five)
+  // before returning to make the panel stays open.
+  // (2) If the panel is not open, check the _state.  It should be either
+  // kStateUninitialized or kStateHidden.  If it's not, then the panel is in the
+  // process of opening -- or maybe it's stuck in that process -- so reset the
+  // _state to kStateHidden.
+  // (3) If the _state is not kStateUninitialized or kStateHidden, then it may
+  // actually be properly opening and not stuck at all.  To avoid always closing
+  // the panel while it's properly opening, use an exponential backoff mechanism
+  // for retries.
+  //
+  // If all that fails, then the test will time out, but it would have timed out
+  // anyway.
+
+  await promiseFocus();
+  await new Promise(resolve => {
+    let verifyCount = 5;
+    let backoff = 0;
+    let iBackoff = 0;
+    let interval = setInterval(() => {
+      if (DownloadsPanel.panel && DownloadsPanel.panel.state == "open") {
+        if (verifyCount > 0) {
+          verifyCount--;
+        } else {
+          clearInterval(interval);
+          resolve();
+        }
+      } else if (iBackoff < backoff) {
+        // Keep backing off before trying again.
+        iBackoff++;
+      } else {
+        // Try (or retry) opening the panel.
+        verifyCount = 5;
+        backoff = Math.max(1, 2 * backoff);
+        iBackoff = 0;
+        if (DownloadsPanel._state != DownloadsPanel.kStateUninitialized) {
+          DownloadsPanel._state = DownloadsPanel.kStateHidden;
+        }
+        DownloadsPanel.showPanel();
+      }
+    }, 100);
+  });
+}
+
+function promisePanelHidden() {
+  return BrowserTestUtils.waitForEvent(DownloadsPanel.panel, "popuphidden");
+}
+
+function makeDownload(verdict) {
+  return {
+    state: DownloadsCommon.DOWNLOAD_DIRTY,
+    hasBlockedData: true,
+    errorObj: {
+      result: Cr.NS_ERROR_FAILURE,
+      message: "Download blocked.",
+      becauseBlocked: true,
+      becauseBlockedByReputationCheck: true,
+      reputationCheckVerdict: verdict,
+    },
+  };
+}
+
+function promiseViewShown(view) {
+  return BrowserTestUtils.waitForEvent(view, "ViewShown");
+}
+
+function promiseUnblockAndSaveCalled(item) {
+  return new Promise(resolve => {
+    let realFn = item._shell.unblockAndSave;
+    item._shell.unblockAndSave = async () => {
+      item._shell.unblockAndSave = realFn;
+      resolve();
+    };
+  });
+}
diff --git a/browser/components/downloads/test/browser/browser_downloads_panel_context_menu.js b/browser/components/downloads/test/browser/browser_downloads_panel_context_menu.js
new file mode 100644
index 0000000000..c5deb992a9
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_downloads_panel_context_menu.js
@@ -0,0 +1,595 @@
+/*
+  Coverage for context menu state for downloads in the Downloads Panel
+*/
+
+let gDownloadDir;
+const TestFiles = {};
+
+let ReferrerInfo = Components.Constructor(
+  "@mozilla.org/referrer-info;1",
+  "nsIReferrerInfo",
+  "init"
+);
+
+// Load a new URI with a specific referrer.
+let exampleRefInfo = new ReferrerInfo(
+  Ci.nsIReferrerInfo.EMPTY,
+  true,
+  Services.io.newURI("https://example.org")
+);
+
+const MENU_ITEMS = {
+  pause: ".downloadPauseMenuItem",
+  resume: ".downloadResumeMenuItem",
+  unblock: '[command="downloadsCmd_unblock"]',
+  openInSystemViewer: '[command="downloadsCmd_openInSystemViewer"]',
+  alwaysOpenInSystemViewer: '[command="downloadsCmd_alwaysOpenInSystemViewer"]',
+  alwaysOpenSimilarFiles: '[command="downloadsCmd_alwaysOpenSimilarFiles"]',
+  show: '[command="downloadsCmd_show"]',
+  commandsSeparator: "menuseparator,.downloadCommandsSeparator",
+  openReferrer: ".downloadOpenReferrerMenuItem",
+  copyLocation: ".downloadCopyLocationMenuItem",
+  separator: "menuseparator",
+  deleteFile: ".downloadDeleteFileMenuItem",
+  delete: '[command="cmd_delete"]',
+  clearList: '[command="downloadsCmd_clearList"]',
+  clearDownloads: '[command="downloadsCmd_clearDownloads"]',
+};
+
+const TestCasesDefaultMimetypes = [
+  {
+    name: "Completed PDF download with improvements pref disabled",
+    prefEnabled: false,
+    downloads: [
+      {
+        state: DownloadsCommon.DOWNLOAD_FINISHED,
+        contentType: "application/pdf",
+        target: {},
+        source: {
+          referrerInfo: exampleRefInfo,
+        },
+      },
+    ],
+    expected: {
+      menu: [
+        MENU_ITEMS.openInSystemViewer,
+        MENU_ITEMS.alwaysOpenInSystemViewer,
+        MENU_ITEMS.show,
+        MENU_ITEMS.commandsSeparator,
+        MENU_ITEMS.openReferrer,
+        MENU_ITEMS.copyLocation,
+        MENU_ITEMS.separator,
+        MENU_ITEMS.deleteFile,
+        MENU_ITEMS.delete,
+        MENU_ITEMS.clearList,
+      ],
+    },
+  },
+  {
+    name:
+      "Completed PDF download with improvements pref disabled and referrer info missing",
+    prefEnabled: false,
+    downloads: [
+      {
+        state: DownloadsCommon.DOWNLOAD_FINISHED,
+        contentType: "application/pdf",
+        target: {},
+      },
+    ],
+    expected: {
+      menu: [
+        MENU_ITEMS.openInSystemViewer,
+        MENU_ITEMS.alwaysOpenInSystemViewer,
+        MENU_ITEMS.show,
+        MENU_ITEMS.commandsSeparator,
+        MENU_ITEMS.copyLocation,
+        MENU_ITEMS.separator,
+        MENU_ITEMS.deleteFile,
+        MENU_ITEMS.delete,
+        MENU_ITEMS.clearList,
+      ],
+    },
+  },
+  {
+    name: "Canceled PDF download with improvements pref disabled",
+    prefEnabled: false,
+    downloads: [
+      {
+        state: DownloadsCommon.DOWNLOAD_CANCELED,
+        contentType: "application/pdf",
+        target: {},
+        source: {
+          referrerInfo: exampleRefInfo,
+        },
+      },
+    ],
+    expected: {
+      menu: [
+        MENU_ITEMS.openReferrer,
+        MENU_ITEMS.copyLocation,
+        MENU_ITEMS.separator,
+        MENU_ITEMS.delete,
+        MENU_ITEMS.clearList,
+      ],
+    },
+  },
+];
+
+const TestCasesNewMimetypesPrefDisabled = [
+  {
+    name: "Completed txt download with improvements pref disabled",
+    prefEnabled: false,
+    downloads: [
+      {
+        state: DownloadsCommon.DOWNLOAD_FINISHED,
+        contentType: "text/plain",
+        target: {},
+        source: {
+          referrerInfo: exampleRefInfo,
+        },
+      },
+    ],
+    expected: {
+      menu: [
+        MENU_ITEMS.show,
+        MENU_ITEMS.commandsSeparator,
+        MENU_ITEMS.openReferrer,
+        MENU_ITEMS.copyLocation,
+        MENU_ITEMS.separator,
+        MENU_ITEMS.deleteFile,
+        MENU_ITEMS.delete,
+        MENU_ITEMS.clearList,
+      ],
+    },
+  },
+  {
+    name: "Canceled txt download with improvements pref disabled",
+    prefEnabled: false,
+    downloads: [
+      {
+        state: DownloadsCommon.DOWNLOAD_CANCELED,
+        contentType: "text/plain",
+        target: {},
+        source: {
+          referrerInfo: exampleRefInfo,
+        },
+      },
+    ],
+    expected: {
+      menu: [
+        MENU_ITEMS.openReferrer,
+        MENU_ITEMS.copyLocation,
+        MENU_ITEMS.separator,
+        MENU_ITEMS.delete,
+        MENU_ITEMS.clearList,
+      ],
+    },
+  },
+];
+
+const TestCasesNewMimetypesPrefEnabled = [
+  {
+    name: "Completed txt download with improvements pref enabled",
+    prefEnabled: true,
+    downloads: [
+      {
+        state: DownloadsCommon.DOWNLOAD_FINISHED,
+        contentType: "text/plain",
+        target: {},
+        source: {
+          referrerInfo: exampleRefInfo,
+        },
+      },
+    ],
+    expected: {
+      menu: [
+        MENU_ITEMS.alwaysOpenSimilarFiles,
+        MENU_ITEMS.show,
+        MENU_ITEMS.commandsSeparator,
+        MENU_ITEMS.openReferrer,
+        MENU_ITEMS.copyLocation,
+        MENU_ITEMS.separator,
+        MENU_ITEMS.deleteFile,
+        MENU_ITEMS.delete,
+        MENU_ITEMS.clearList,
+      ],
+    },
+  },
+  {
+    name: "Canceled txt download with improvements pref enabled",
+    prefEnabled: true,
+    downloads: [
+      {
+        state: DownloadsCommon.DOWNLOAD_CANCELED,
+        contentType: "text/plain",
+        target: {},
+        source: {
+          referrerInfo: exampleRefInfo,
+        },
+      },
+    ],
+    expected: {
+      menu: [
+        MENU_ITEMS.openReferrer,
+        MENU_ITEMS.copyLocation,
+        MENU_ITEMS.separator,
+        MENU_ITEMS.delete,
+        MENU_ITEMS.clearList,
+      ],
+    },
+  },
+  {
+    name:
+      "Completed unknown ext download with application/octet-stream and improvements pref enabled",
+    prefEnabled: true,
+    overrideExtension: "unknownExtension",
+    downloads: [
+      {
+        state: DownloadsCommon.DOWNLOAD_FINISHED,
+        contentType: "application/octet-stream",
+        target: {},
+        source: {
+          referrerInfo: exampleRefInfo,
+        },
+      },
+    ],
+    expected: {
+      menu: [
+        MENU_ITEMS.show,
+        MENU_ITEMS.commandsSeparator,
+        MENU_ITEMS.openReferrer,
+        MENU_ITEMS.copyLocation,
+        MENU_ITEMS.separator,
+        MENU_ITEMS.deleteFile,
+        MENU_ITEMS.delete,
+        MENU_ITEMS.clearList,
+      ],
+    },
+  },
+  {
+    name:
+      "Completed txt download with application/octet-stream and improvements pref enabled",
+    prefEnabled: true,
+    overrideExtension: "txt",
+    downloads: [
+      {
+        state: DownloadsCommon.DOWNLOAD_FINISHED,
+        contentType: "application/octet-stream",
+        target: {},
+        source: {
+          referrerInfo: exampleRefInfo,
+        },
+      },
+    ],
+    expected: {
+      menu: [
+        // Despite application/octet-stream content type, ensure
+        // alwaysOpenSimilarFiles still appears since txt files
+        // are supported file types.
+        MENU_ITEMS.alwaysOpenSimilarFiles,
+        MENU_ITEMS.show,
+        MENU_ITEMS.commandsSeparator,
+        MENU_ITEMS.openReferrer,
+        MENU_ITEMS.copyLocation,
+        MENU_ITEMS.separator,
+        MENU_ITEMS.deleteFile,
+        MENU_ITEMS.delete,
+        MENU_ITEMS.clearList,
+      ],
+    },
+  },
+];
+
+const TestCasesDeletedFile = [
+  {
+    name: "Download with file deleted and improvements pref enabled",
+    prefEnabled: true,
+    downloads: [
+      {
+        state: DownloadsCommon.DOWNLOAD_FINISHED,
+        contentType: "text/plain",
+        target: {},
+        source: {
+          referrerInfo: exampleRefInfo,
+        },
+        deleted: true,
+      },
+    ],
+    expected: {
+      menu: [
+        MENU_ITEMS.alwaysOpenSimilarFiles,
+        MENU_ITEMS.openReferrer,
+        MENU_ITEMS.copyLocation,
+        MENU_ITEMS.separator,
+        MENU_ITEMS.delete,
+        MENU_ITEMS.clearList,
+      ],
+    },
+  },
+];
+
+const TestCasesMultipleFiles = [
+  {
+    name: "Multiple files",
+    prefEnabled: true,
+    downloads: [
+      {
+        state: DownloadsCommon.DOWNLOAD_FINISHED,
+        contentType: "text/plain",
+        target: {},
+        source: {
+          referrerInfo: exampleRefInfo,
+        },
+      },
+      {
+        state: DownloadsCommon.DOWNLOAD_FINISHED,
+        contentType: "text/plain",
+        target: {},
+        source: {
+          referrerInfo: exampleRefInfo,
+        },
+        deleted: true,
+      },
+    ],
+    expected: {
+      menu: [
+        MENU_ITEMS.alwaysOpenSimilarFiles,
+        MENU_ITEMS.openReferrer,
+        MENU_ITEMS.copyLocation,
+        MENU_ITEMS.separator,
+        MENU_ITEMS.delete,
+        MENU_ITEMS.clearList,
+      ],
+    },
+    itemIndex: 1,
+  },
+];
+
+add_setup(async function() {
+  // remove download files, empty out collections
+  let downloadList = await Downloads.getList(Downloads.ALL);
+  let downloadCount = (await downloadList.getAll()).length;
+  is(downloadCount, 0, "At the start of the test, there should be 0 downloads");
+
+  await task_resetState();
+  if (!gDownloadDir) {
+    gDownloadDir = await setDownloadDir();
+  }
+  info("Created download directory: " + gDownloadDir);
+
+  // create the downloaded files we'll need
+  TestFiles.pdf = await createDownloadedFile(
+    PathUtils.join(gDownloadDir, "downloaded.pdf"),
+    DATA_PDF
+  );
+  info("Created downloaded PDF file at:" + TestFiles.pdf.path);
+  TestFiles.txt = await createDownloadedFile(
+    PathUtils.join(gDownloadDir, "downloaded.txt"),
+    "Test file"
+  );
+  info("Created downloaded text file at:" + TestFiles.txt.path);
+  TestFiles.unknownExtension = await createDownloadedFile(
+    PathUtils.join(gDownloadDir, "downloaded.unknownExtension"),
+    "Test file"
+  );
+  info(
+    "Created downloaded unknownExtension file at:" +
+      TestFiles.unknownExtension.path
+  );
+  TestFiles.nonexistentFile = new FileUtils.File(
+    PathUtils.join(gDownloadDir, "nonexistent")
+  );
+  info(
+    "Created nonexistent downloaded file at:" + TestFiles.nonexistentFile.path
+  );
+});
+
+// register the tests
+for (let testData of TestCasesDefaultMimetypes) {
+  if (testData.skip) {
+    info("Skipping test:" + testData.name);
+    continue;
+  }
+  // use the 'name' property of each test case as the test function name
+  // so we get useful logs
+  let tmp = {
+    async [testData.name]() {
+      await testDownloadContextMenu(testData);
+    },
+  };
+  add_task(tmp[testData.name]);
+}
+
+// non default mimetypes with browser.download.improvements_to_download_panel disabled
+for (let testData of TestCasesNewMimetypesPrefDisabled) {
+  if (testData.skip) {
+    info("Skipping test:" + testData.name);
+    continue;
+  }
+  // use the 'name' property of each test case as the test function name
+  // so we get useful logs
+  let tmp = {
+    async [testData.name]() {
+      await testDownloadContextMenu(testData);
+    },
+  };
+  add_task(tmp[testData.name]);
+}
+
+// non default mimetypes with browser.download.improvements_to_download_panel enabled
+for (let testData of TestCasesNewMimetypesPrefEnabled) {
+  if (testData.skip) {
+    info("Skipping test:" + testData.name);
+    continue;
+  }
+  // use the 'name' property of each test case as the test function name
+  // so we get useful logs
+  let tmp = {
+    async [testData.name]() {
+      await testDownloadContextMenu(testData);
+    },
+  };
+  add_task(tmp[testData.name]);
+}
+
+for (let testData of TestCasesDeletedFile) {
+  if (testData.skip) {
+    info("Skipping test:" + testData.name);
+    continue;
+  }
+  // use the 'name' property of each test case as the test function name
+  // so we get useful logs
+  let tmp = {
+    async [testData.name]() {
+      await testDownloadContextMenu(testData);
+    },
+  };
+  add_task(tmp[testData.name]);
+}
+
+for (let testData of TestCasesMultipleFiles) {
+  if (testData.skip) {
+    info("Skipping test:" + testData.name);
+    continue;
+  }
+  // use the 'name' property of each test case as the test function name
+  // so we get useful logs
+  let tmp = {
+    async [testData.name]() {
+      await testDownloadContextMenu(testData);
+    },
+  };
+  add_task(tmp[testData.name]);
+}
+
+async function testDownloadContextMenu({
+  overrideExtension = null,
+  downloads = [],
+  expected,
+  prefEnabled,
+  itemIndex = 0,
+}) {
+  info(
+    `Setting browser.download.improvements_to_download_panel to ${prefEnabled}`
+  );
+  SpecialPowers.setBoolPref(
+    "browser.download.improvements_to_download_panel",
+    prefEnabled
+  );
+  // prepare downloads
+  await prepareDownloads(downloads, overrideExtension);
+  let downloadList = await Downloads.getList(Downloads.PUBLIC);
+  let download = (await downloadList.getAll())[itemIndex];
+  info("Download succeeded? " + download.succeeded);
+  info("Download target exists? " + download.target.exists);
+
+  // open panel
+  await task_openPanel();
+  await TestUtils.waitForCondition(() => {
+    let downloadsListBox = document.getElementById("downloadsListBox");
+    downloadsListBox.removeAttribute("disabled");
+    return downloadsListBox.childElementCount == downloads.length;
+  });
+
+  let itemTarget = document
+    .querySelectorAll("#downloadsListBox richlistitem")
+    [itemIndex].querySelector(".downloadMainArea");
+  EventUtils.synthesizeMouse(itemTarget, 1, 1, { type: "mousemove" });
+  is(
+    DownloadsView.richListBox.selectedIndex,
+    0,
+    "moving the mouse resets the richlistbox's selected index"
+  );
+
+  info("trigger the context menu");
+  let contextMenu = await openContextMenu(itemTarget);
+
+  // FIXME: This works in practice, but simulating the context menu opening
+  // doesn't seem to automatically set the selected index.
+  DownloadsView.richListBox.selectedIndex = itemIndex;
+  EventUtils.synthesizeMouse(itemTarget, 1, 1, { type: "mousemove" });
+  is(
+    DownloadsView.richListBox.selectedIndex,
+    itemIndex,
+    "selected index after opening the context menu and moving the mouse"
+  );
+
+  info("context menu should be open, verify its menu items");
+  let result = verifyContextMenu(contextMenu, expected.menu);
+
+  // close menus
+  contextMenu.hidePopup();
+  let hiddenPromise = BrowserTestUtils.waitForEvent(
+    DownloadsPanel.panel,
+    "popuphidden"
+  );
+  DownloadsPanel.hidePanel();
+  await hiddenPromise;
+
+  ok(!result, "Expected no errors verifying context menu items");
+
+  // clean up downloads
+  await downloadList.removeFinished();
+}
+
+// ----------------------------------------------------------------------------
+// Helpers
+
+function verifyContextMenu(contextMenu, itemSelectors) {
+  // Ignore hidden nodes
+  let items = Array.from(contextMenu.children).filter(n =>
+    BrowserTestUtils.is_visible(n)
+  );
+  let menuAsText = items
+    .map(n => {
+      return n.nodeName == "menuseparator"
+        ? "---"
+        : `${n.label} (${n.command})`;
+    })
+    .join("\n");
+  info("Got actual context menu items: \n" + menuAsText);
+
+  try {
+    is(
+      items.length,
+      itemSelectors.length,
+      "Context menu has the expected number of items"
+    );
+    for (let i = 0; i < items.length; i++) {
+      let selector = itemSelectors[i];
+      ok(
+        items[i].matches(selector),
+        `Item at ${i} matches expected selector: ${selector}`
+      );
+    }
+  } catch (ex) {
+    return ex;
+  }
+  return null;
+}
+
+async function prepareDownloads(downloads, overrideExtension = null) {
+  for (let props of downloads) {
+    info(JSON.stringify(props));
+    if (props.state !== DownloadsCommon.DOWNLOAD_FINISHED) {
+      continue;
+    }
+    if (props.deleted) {
+      props.target = TestFiles.nonexistentFile;
+      continue;
+    }
+    switch (props.contentType) {
+      case "application/pdf":
+        props.target = TestFiles.pdf;
+        break;
+      case "text/plain":
+        props.target = TestFiles.txt;
+        break;
+      case "application/octet-stream":
+        props.target = TestFiles[overrideExtension];
+        break;
+    }
+    ok(props.target instanceof Ci.nsIFile, "download target is a nsIFile");
+  }
+  await task_addDownloads(downloads);
+}
diff --git a/browser/components/downloads/test/browser/browser_downloads_panel_ctrl_click.js b/browser/components/downloads/test/browser/browser_downloads_panel_ctrl_click.js
new file mode 100644
index 0000000000..57ef284bc1
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_downloads_panel_ctrl_click.js
@@ -0,0 +1,35 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+add_task(async function test_downloads_panel() {
+  // On macOS, ctrl-click shouldn't open the panel because this normally opens
+  // the context menu. This happens via the `contextmenu` event which is created
+  // by widget code, so our simulated clicks do not do so, so we can't test
+  // anything on macOS.
+  if (AppConstants.platform == "macosx") {
+    ok(true, "The test is ignored on Mac");
+    return;
+  }
+
+  await SpecialPowers.pushPrefEnv({
+    set: [["browser.download.autohideButton", false]],
+  });
+  await promiseButtonShown("downloads-button");
+
+  const button = document.getElementById("downloads-button");
+  let shownPromise = promisePanelOpened();
+  // Should still open the panel when Ctrl key is pressed.
+  EventUtils.synthesizeMouseAtCenter(button, { ctrlKey: true });
+  await shownPromise;
+  is(DownloadsPanel.panel.state, "open", "Check that panel state is 'open'");
+
+  // Close download panel
+  DownloadsPanel.hidePanel();
+  is(
+    DownloadsPanel.panel.state,
+    "closed",
+    "Check that panel state is 'closed'"
+  );
+});
diff --git a/browser/components/downloads/test/browser/browser_downloads_panel_disable_items.js b/browser/components/downloads/test/browser/browser_downloads_panel_disable_items.js
new file mode 100644
index 0000000000..ba4f31e8b4
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_downloads_panel_disable_items.js
@@ -0,0 +1,172 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const TEST_URI = "https://example.com";
+const TEST_PATH = getRootDirectory(gTestPath).replace(
+  "chrome://mochitests/content",
+  TEST_URI
+);
+
+add_setup(async function() {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["browser.download.improvements_to_download_panel", true],
+      ["browser.download.alwaysOpenPanel", true],
+      ["browser.download.always_ask_before_handling_new_types", false],
+      ["security.dialog_enable_delay", 1000],
+    ],
+  });
+  // Remove download files from previous tests
+  await task_resetState();
+  let downloadList = await Downloads.getList(Downloads.ALL);
+  let downloadCount = (await downloadList.getAll()).length;
+  is(downloadCount, 0, "At the start of the test, there should be 0 downloads");
+});
+
+/**
+ * Tests that the download items remain enabled when we manually open
+ * the downloads panel by clicking the downloads button.
+ */
+add_task(async function test_downloads_panel_downloads_button() {
+  let panelOpenedPromise = promisePanelOpened();
+  await task_addDownloads([{ state: DownloadsCommon.DOWNLOAD_FINISHED }]);
+  await panelOpenedPromise;
+
+  // The downloads panel will open automatically after task_addDownloads
+  // creates a download file. Let's close the panel and reopen it again
+  // (but this time manually) to ensure the download items are not disabled.
+  DownloadsPanel.hidePanel();
+
+  ok(!DownloadsPanel.isPanelShowing, "Downloads Panel should not be visible");
+
+  info("Manually open the download panel to view list of downloads");
+  let downloadsButton = document.getElementById("downloads-button");
+  EventUtils.synthesizeMouseAtCenter(downloadsButton, {});
+  let downloadsListBox = document.getElementById("downloadsListBox");
+
+  ok(downloadsListBox, "downloadsListBox richlistitem should be visible");
+  is(
+    downloadsListBox.childElementCount,
+    1,
+    "downloadsListBox should have 1 download"
+  );
+  ok(
+    !downloadsListBox.getAttribute("disabled"),
+    "All download items in the downloads panel should not be disabled"
+  );
+
+  info("Cleaning up downloads");
+  await task_resetState();
+});
+
+/**
+ * Tests that the download items are disabled when the downloads panel is
+ * automatically opened as a result of a new download.
+ */
+add_task(async function test_downloads_panel_new_download() {
+  // Overwrite DownloadsCommon.openDownload to prevent file from opening during tests
+  const originalOpenDownload = DownloadsCommon.openDownload;
+  DownloadsCommon.openDownload = async () => {
+    ok(false, "openDownload was called when it was not expected");
+  };
+  let newTabPromise = BrowserTestUtils.openNewForegroundTab({
+    gBrowser,
+    opening: TEST_PATH + "foo.txt",
+    waitForLoad: false,
+    waitForStateStop: true,
+  });
+
+  await promisePanelOpened();
+  let downloadsListBox = document.getElementById("downloadsListBox");
+
+  ok(downloadsListBox, "downloadsListBox richlistitem should be visible");
+  await BrowserTestUtils.waitForMutationCondition(
+    downloadsListBox,
+    { childList: true },
+    () => downloadsListBox.childElementCount == 1
+  );
+  info("downloadsListBox should have 1 download");
+  ok(
+    downloadsListBox.getAttribute("disabled"),
+    "All download items in the downloads panel should first be disabled"
+  );
+
+  let newTab = await newTabPromise;
+
+  // Press enter 6 times at 100ms intervals.
+  EventUtils.synthesizeKey("KEY_Enter", {}, window);
+  for (let i = 0; i < 5; i++) {
+    // There's no other way to allow some time to pass and ensure we're
+    // genuinely testing that these keypresses postpone the enabling of
+    // the items, so disable this check for this line:
+    // eslint-disable-next-line mozilla/no-arbitrary-setTimeout
+    await new Promise(r => setTimeout(r, 100));
+    EventUtils.synthesizeKey("KEY_Enter", {}, window);
+  }
+  // Measure when we finished.
+  let keyTime = Date.now();
+
+  await BrowserTestUtils.waitForMutationCondition(
+    downloadsListBox,
+    { attributeFilter: ["disabled"] },
+    () => !downloadsListBox.hasAttribute("disabled")
+  );
+  Assert.greater(
+    Date.now(),
+    keyTime + 750,
+    "Should have waited at least another 750ms after this keypress."
+  );
+  let openedDownload = new Promise(resolve => {
+    DownloadsCommon.openDownload = async () => {
+      ok(true, "openDownload should have been called");
+      resolve();
+    };
+  });
+
+  info("All download items in the download panel should now be enabled");
+  EventUtils.synthesizeKey("KEY_Enter", {}, window);
+  await openedDownload;
+
+  await task_resetState();
+  DownloadsCommon.openDownload = originalOpenDownload;
+  BrowserTestUtils.removeTab(newTab);
+});
+
+/**
+ * Tests that the disabled attribute does not exist when we close the
+ * downloads panel before the disabled state timeout resolves.
+ */
+add_task(async function test_downloads_panel_close_panel_early() {
+  info("Creating mock completed downloads");
+  await task_addDownloads([{ state: DownloadsCommon.DOWNLOAD_FINISHED }]);
+
+  // The downloads panel may open automatically after task_addDownloads
+  // creates a download file. Let's close the panel and reopen it again
+  // (but this time manually).
+  DownloadsPanel.hidePanel();
+
+  ok(!DownloadsPanel.isPanelShowing, "Downloads Panel should not be visible");
+
+  info("Manually open the download panel to view list of downloads");
+  let downloadsButton = document.getElementById("downloads-button");
+  EventUtils.synthesizeMouseAtCenter(downloadsButton, {});
+  let downloadsListBox = document.getElementById("downloadsListBox");
+
+  ok(downloadsListBox, "downloadsListBox richlistitem should be visible");
+  is(
+    downloadsListBox.childElementCount,
+    1,
+    "downloadsListBox should have 1 download"
+  );
+
+  DownloadsPanel.hidePanel();
+  await BrowserTestUtils.waitForCondition(
+    () => !downloadsListBox.getAttribute("disabled")
+  );
+  info("downloadsListBox 'disabled' attribute should not exist");
+
+  info("Cleaning up downloads");
+  await task_resetState();
+});
diff --git a/browser/components/downloads/test/browser/browser_downloads_panel_dontshow.js b/browser/components/downloads/test/browser/browser_downloads_panel_dontshow.js
new file mode 100644
index 0000000000..b6de758723
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_downloads_panel_dontshow.js
@@ -0,0 +1,126 @@
+// This test verifies that the download panel opens when a
+// download occurs but not when a user manually saves a page.
+
+let MockFilePicker = SpecialPowers.MockFilePicker;
+MockFilePicker.init(window);
+
+async function promiseDownloadFinished(list) {
+  return new Promise(resolve => {
+    list.addView({
+      onDownloadChanged(download) {
+        download.launchWhenSucceeded = false;
+        if (download.succeeded || download.error) {
+          list.removeView(this);
+          resolve(download);
+        }
+      },
+    });
+  });
+}
+
+function openTestPage() {
+  return BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    `https://www.example.com/document-builder.sjs?html=
+      <html><body>
+        <a id='normallink' href='https://www.example.com'>Link1</a>
+        <a id='downloadlink' href='https://www.example.com' download='file.txt'>Link2</a>
+      </body</html>
+    `
+  );
+}
+
+add_task(async function download_saveas_file() {
+  let tab = await openTestPage();
+
+  for (let testname of ["save link", "save page"]) {
+    if (testname == "save link") {
+      let menu = document.getElementById("contentAreaContextMenu");
+      let popupShown = BrowserTestUtils.waitForEvent(menu, "popupshown");
+      BrowserTestUtils.synthesizeMouse(
+        "#normallink",
+        5,
+        5,
+        { type: "contextmenu", button: 2 },
+        gBrowser.selectedBrowser
+      );
+      await popupShown;
+    }
+
+    let list = await Downloads.getList(Downloads.PUBLIC);
+    let downloadFinishedPromise = promiseDownloadFinished(list);
+
+    let saveFile = Services.dirsvc.get("TmpD", Ci.nsIFile);
+    saveFile.append("testsavedir");
+    if (!saveFile.exists()) {
+      saveFile.create(Ci.nsIFile.DIRECTORY_TYPE, 0o755);
+    }
+
+    await new Promise(resolve => {
+      MockFilePicker.showCallback = function(fp) {
+        saveFile.append("sample");
+        MockFilePicker.setFiles([saveFile]);
+        setTimeout(() => {
+          resolve(fp.defaultString);
+        }, 0);
+        return Ci.nsIFilePicker.returnOK;
+      };
+
+      if (testname == "save link") {
+        let menu = document.getElementById("contentAreaContextMenu");
+        let menuitem = document.getElementById("context-savelink");
+        menu.activateItem(menuitem);
+      } else if (testname == "save page") {
+        document.getElementById("Browser:SavePage").doCommand();
+      }
+    });
+
+    await downloadFinishedPromise;
+    is(
+      DownloadsPanel.panel.state,
+      "closed",
+      "downloads panel closed after download link after " + testname
+    );
+  }
+
+  await task_resetState();
+
+  MockFilePicker.cleanup();
+  BrowserTestUtils.removeTab(tab);
+});
+
+add_task(async function download_link() {
+  let tab = await openTestPage();
+
+  let list = await Downloads.getList(Downloads.PUBLIC);
+  let downloadFinishedPromise = promiseDownloadFinished(list);
+
+  let panelOpenedPromise = promisePanelOpened();
+
+  BrowserTestUtils.synthesizeMouse(
+    "#downloadlink",
+    5,
+    5,
+    {},
+    gBrowser.selectedBrowser
+  );
+
+  let download = await downloadFinishedPromise;
+  await panelOpenedPromise;
+
+  is(
+    DownloadsPanel.panel.state,
+    "open",
+    "downloads panel open after download link clicked"
+  );
+
+  DownloadsPanel.hidePanel();
+
+  await task_resetState();
+
+  BrowserTestUtils.removeTab(tab);
+
+  try {
+    await IOUtils.remove(download.target.path);
+  } catch (ex) {}
+});
diff --git a/browser/components/downloads/test/browser/browser_downloads_panel_focus.js b/browser/components/downloads/test/browser/browser_downloads_panel_focus.js
new file mode 100644
index 0000000000..2050e0640b
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_downloads_panel_focus.js
@@ -0,0 +1,111 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+add_setup(async function() {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["browser.download.improvements_to_download_panel", true],
+      ["browser.download.always_ask_before_handling_new_types", false],
+    ],
+  });
+
+  registerCleanupFunction(async () => {
+    info("Resetting downloads and closing downloads panel");
+    await task_resetState();
+  });
+
+  let downloadList = await Downloads.getList(Downloads.ALL);
+  let downloadCount = (await downloadList.getAll()).length;
+  is(downloadCount, 0, "At the start of the test, there should be 0 downloads");
+});
+
+// Test that the top item in the panel always gets focus upon opening the panel.
+add_task(async function test_focus() {
+  info("creating a download and setting it to in progress");
+  await task_addDownloads([{ state: DownloadsCommon.DOWNLOAD_DOWNLOADING }]);
+  let publicList = await Downloads.getList(Downloads.PUBLIC);
+  let downloads = await publicList.getAll();
+  downloads[0].stopped = false;
+
+  info("waiting for the panel to open");
+  await task_openPanel();
+  await BrowserTestUtils.waitForCondition(
+    () => !DownloadsView.richListBox.getAttribute("disabled")
+  );
+
+  is(
+    DownloadsView.richListBox.itemCount,
+    1,
+    "there should be exactly one download listed"
+  );
+  // Most of the time if we want to check which thing has focus, we can just ask
+  // Services.focus to tell us. But the downloads panel uses a <richlistbox>,
+  // and when an item in one of those has focus, the focus manager actually
+  // thinks that *the list itself* has focus, and everything below that is
+  // handled within the widget. So, the best we can do is check that the list is
+  // focused and then that the selected item within the list is correct.
+  is(
+    Services.focus.focusedElement,
+    DownloadsView.richListBox,
+    "the downloads list should have focus"
+  );
+  is(
+    DownloadsView.richListBox.itemChildren[0],
+    DownloadsView.richListBox.selectedItem,
+    "the focused item should be the only download in the list"
+  );
+
+  info("closing the panel and creating a second download");
+  DownloadsPanel.hidePanel();
+  await task_addDownloads([{ state: DownloadsCommon.DOWNLOAD_DOWNLOADING }]);
+
+  info("waiting for the panel to open after starting the second download");
+  await task_openPanel();
+  await BrowserTestUtils.waitForCondition(
+    () => !DownloadsView.richListBox.getAttribute("disabled")
+  );
+
+  is(
+    DownloadsView.richListBox.itemCount,
+    2,
+    "there should be two downloads listed"
+  );
+  is(
+    Services.focus.focusedElement,
+    DownloadsView.richListBox,
+    "the downloads list should have focus"
+  );
+  is(
+    DownloadsView.richListBox.itemChildren[0],
+    DownloadsView.richListBox.selectedItem,
+    "the focused item should be the first download in the list"
+  );
+
+  info("closing the panel and creating a third download");
+  DownloadsPanel.hidePanel();
+  await task_addDownloads([{ state: DownloadsCommon.DOWNLOAD_DOWNLOADING }]);
+
+  info("waiting for the panel to open after starting the third download");
+  await task_openPanel();
+  await BrowserTestUtils.waitForCondition(
+    () => !DownloadsView.richListBox.getAttribute("disabled")
+  );
+
+  is(
+    DownloadsView.richListBox.itemCount,
+    3,
+    "there should be three downloads listed"
+  );
+  is(
+    Services.focus.focusedElement,
+    DownloadsView.richListBox,
+    "the downloads list should have focus"
+  );
+  is(
+    DownloadsView.richListBox.itemChildren[0],
+    DownloadsView.richListBox.selectedItem,
+    "the focused item should be the first download in the list"
+  );
+});
diff --git a/browser/components/downloads/test/browser/browser_downloads_panel_height.js b/browser/components/downloads/test/browser/browser_downloads_panel_height.js
new file mode 100644
index 0000000000..b154d20f84
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_downloads_panel_height.js
@@ -0,0 +1,35 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+/**
+ * This test exists because we use a <panelmultiview> element and it handles
+ * some of the height changes for us. We need to verify that the height is
+ * updated correctly if downloads are removed while the panel is hidden.
+ */
+add_task(async function test_height_reduced_after_removal() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["browser.download.autohideButton", false]],
+  });
+  await promiseButtonShown("downloads-button");
+  // downloading two items since the download panel only shows up when at least one item is in it
+  await task_addDownloads([{ state: DownloadsCommon.DOWNLOAD_FINISHED }]);
+  await task_addDownloads([{ state: DownloadsCommon.DOWNLOAD_FINISHED }]);
+
+  await task_openPanel();
+  let panel = document.getElementById("downloadsPanel");
+  let heightBeforeRemoval = panel.getBoundingClientRect().height;
+
+  // We want to close the panel before we remove the download from the list.
+  DownloadsPanel.hidePanel();
+  await task_resetState();
+  // keep at least one item in the download list since the panel disabled when it is empty
+  await task_addDownloads([{ state: DownloadsCommon.DOWNLOAD_FINISHED }]);
+
+  await task_openPanel();
+  let heightAfterRemoval = panel.getBoundingClientRect().height;
+  Assert.greater(heightBeforeRemoval, heightAfterRemoval);
+
+  await task_resetState();
+});
diff --git a/browser/components/downloads/test/browser/browser_downloads_panel_opens.js b/browser/components/downloads/test/browser/browser_downloads_panel_opens.js
new file mode 100644
index 0000000000..fb1e6f76da
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_downloads_panel_opens.js
@@ -0,0 +1,686 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+let { MockFilePicker } = SpecialPowers;
+MockFilePicker.init(window);
+registerCleanupFunction(() => MockFilePicker.cleanup());
+
+/**
+ * Check that the downloads panel opens when a download is spoofed.
+ */
+async function checkPanelOpens() {
+  info("Waiting for panel to open.");
+  let promise = promisePanelOpened();
+  DownloadsCommon.getData(window)._notifyDownloadEvent("start");
+  is(
+    DownloadsPanel.isPanelShowing,
+    true,
+    "Panel state should indicate a preparation to be opened."
+  );
+  await promise;
+
+  is(DownloadsPanel.panel.state, "open", "Panel should be opened.");
+
+  DownloadsPanel.hidePanel();
+}
+
+/**
+ * Start a download and check that the downloads panel opens correctly according
+ * to the download parameter, openDownloadsListOnStart
+ * @param {boolean} [openDownloadsListOnStart]
+ *        true (default) - open downloads panel when download starts
+ *        false - no downloads panel; update indicator attention state
+ */
+async function downloadAndCheckPanel({ openDownloadsListOnStart = true } = {}) {
+  info("creating a download and setting it to in progress");
+  await task_addDownloads([
+    {
+      state: DownloadsCommon.DOWNLOAD_DOWNLOADING,
+      openDownloadsListOnStart,
+    },
+  ]);
+  let publicList = await Downloads.getList(Downloads.PUBLIC);
+  let downloads = await publicList.getAll();
+  downloads[0].stopped = false;
+
+  // Make sure we remove that download at the end of the test.
+  let oldShowEventNotification = DownloadsIndicatorView.showEventNotification;
+  registerCleanupFunction(async () => {
+    for (let download of downloads) {
+      await publicList.remove(download);
+    }
+    DownloadsIndicatorView.showEventNotification = oldShowEventNotification;
+  });
+
+  // Instead of the panel opening, the download notification should be shown.
+  let promiseDownloadStartedNotification = new Promise(resolve => {
+    DownloadsIndicatorView.showEventNotification = aType => {
+      if (aType == "start") {
+        resolve();
+      }
+    };
+  });
+
+  DownloadsCommon.getData(window)._notifyDownloadEvent("start", {
+    openDownloadsListOnStart,
+  });
+  is(
+    DownloadsPanel.isPanelShowing,
+    false,
+    "Panel state should indicate it is not preparing to be opened"
+  );
+
+  info("waiting for download to start");
+  await promiseDownloadStartedNotification;
+
+  DownloadsIndicatorView.showEventNotification = oldShowEventNotification;
+  is(DownloadsPanel.panel.state, "closed", "Panel should be closed");
+}
+
+function clickCheckbox(checkbox) {
+  // Clicking a checkbox toggles its checkedness first.
+  if (checkbox.getAttribute("checked") == "true") {
+    checkbox.removeAttribute("checked");
+  } else {
+    checkbox.setAttribute("checked", "true");
+  }
+  // Then it runs the command and closes the popup.
+  checkbox.doCommand();
+  checkbox.parentElement.hidePopup();
+}
+
+/**
+ * Test that the downloads panel correctly opens or doesn't open based on
+ * whether the download triggered a dialog already. If askWhereToSave is true,
+ * we should get a file picker dialog. If preferredAction is alwaysAsk, we
+ * should get an unknown content type dialog. If neither of those is true, we
+ * should get no dialog at all, and expect the downloads panel to open.
+ * @param {boolean} [expectPanelToOpen] true - fail if panel doesn't open
+ *                                      false (default) - fail if it opens
+ * @param {number}  [preferredAction]   Default download action:
+ *                                      0 (default) - save download to disk
+ *                                      1 - open UCT dialog first
+ * @param {boolean} [askWhereToSave]    true - open file picker dialog
+ *                                      false (default) - use download dir
+ */
+async function testDownloadsPanelAfterDialog({
+  expectPanelToOpen = false,
+  preferredAction,
+  askWhereToSave = false,
+} = {}) {
+  const { saveToDisk, alwaysAsk } = Ci.nsIHandlerInfo;
+  if (![saveToDisk, alwaysAsk].includes(preferredAction)) {
+    preferredAction = saveToDisk;
+  }
+  const openUCT = preferredAction === alwaysAsk;
+  const TEST_PATH = getRootDirectory(gTestPath).replace(
+    "chrome://mochitests/content",
+    "https://example.com"
+  );
+  const MimeSvc = Cc["@mozilla.org/mime;1"].getService(Ci.nsIMIMEService);
+  const HandlerSvc = Cc["@mozilla.org/uriloader/handler-service;1"].getService(
+    Ci.nsIHandlerService
+  );
+  let publicList = await Downloads.getList(Downloads.PUBLIC);
+
+  for (let download of await publicList.getAll()) {
+    await publicList.remove(download);
+  }
+
+  // We need to test the changes from bug 1739348, where the helper app service
+  // sets a flag based on whether a file picker dialog was opened, and this flag
+  // determines whether the downloads panel will be opened as the download
+  // starts. We need to actually hit "Save" for the download to start, but we
+  // can't interact with the real file picker dialog. So this temporarily
+  // replaces it with a barebones component that plugs into the helper app
+  // service and tells it to start saving the file to the default path.
+  if (askWhereToSave) {
+    MockFilePicker.returnValue = MockFilePicker.returnOK;
+    MockFilePicker.showCallback = function(fp) {
+      // Get the default location from the helper app service.
+      let testFile = MockFilePicker.displayDirectory.clone();
+      testFile.append(fp.defaultString);
+      info("File picker download path: " + testFile.path);
+      MockFilePicker.setFiles([testFile]);
+      MockFilePicker.filterIndex = 0; // kSaveAsType_Complete
+      MockFilePicker.showCallback = null;
+      // Confirm that saving should proceed. The helper app service uses this
+      // value to determine whether to invoke launcher.saveDestinationAvailable
+      return MockFilePicker.returnOK;
+    };
+  }
+
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["browser.download.useDownloadDir", !askWhereToSave],
+      ["browser.download.always_ask_before_handling_new_types", openUCT],
+      ["browser.download.improvements_to_download_panel", true],
+      ["security.dialog_enable_delay", 0],
+    ],
+  });
+
+  // Configure the handler for the file according to parameters.
+  let mimeInfo = MimeSvc.getFromTypeAndExtension("text/plain", "txt");
+  let existed = HandlerSvc.exists(mimeInfo);
+  mimeInfo.alwaysAskBeforeHandling = openUCT;
+  mimeInfo.preferredAction = preferredAction;
+  HandlerSvc.store(mimeInfo);
+  registerCleanupFunction(async () => {
+    // Reset the handler to its original state.
+    if (existed) {
+      HandlerSvc.store(mimeInfo);
+    } else {
+      HandlerSvc.remove(mimeInfo);
+    }
+    await publicList.removeFinished();
+    BrowserTestUtils.removeTab(loadingTab);
+  });
+
+  let dialogWindowPromise = BrowserTestUtils.domWindowOpenedAndLoaded();
+  let downloadFinishedPromise = new Promise(resolve => {
+    publicList.addView({
+      onDownloadChanged(download) {
+        info("Download changed!");
+        if (download.succeeded || download.error) {
+          info("Download succeeded or failed.");
+          publicList.removeView(this);
+          resolve(download);
+        }
+      },
+    });
+  });
+  let panelOpenedPromise = expectPanelToOpen ? promisePanelOpened() : null;
+
+  // Open the tab that will trigger the download.
+  let loadingTab = await BrowserTestUtils.openNewForegroundTab({
+    gBrowser,
+    opening: TEST_PATH + "foo.txt",
+    waitForLoad: false,
+    waitForStateStop: true,
+  });
+
+  // Wait for a UCT dialog if the handler was set up to open one.
+  if (openUCT) {
+    let dialogWindow = await dialogWindowPromise;
+    is(
+      dialogWindow.location.href,
+      "chrome://mozapps/content/downloads/unknownContentType.xhtml",
+      "Should have seen the unknown content dialogWindow."
+    );
+    let doc = dialogWindow.document;
+    let dialog = doc.getElementById("unknownContentType");
+    let radio = doc.getElementById("save");
+    let button = dialog.getButton("accept");
+
+    await TestUtils.waitForCondition(
+      () => !button.disabled,
+      "Waiting for the UCT dialog's Accept button to be enabled."
+    );
+    ok(!radio.hidden, "The Save option should be visible");
+    // Make sure we aren't opening the file.
+    radio.click();
+    ok(radio.selected, "The Save option should be selected");
+    button.disabled = false;
+    dialog.acceptDialog();
+  }
+
+  info("Waiting for download to finish.");
+  let download = await downloadFinishedPromise;
+  ok(!download.error, "There should be no error.");
+  is(
+    DownloadsPanel.isPanelShowing,
+    expectPanelToOpen,
+    `Panel should${expectPanelToOpen ? " " : " not "}be showing.`
+  );
+  if (DownloadsPanel.isPanelShowing) {
+    await panelOpenedPromise;
+    let hiddenPromise = BrowserTestUtils.waitForPopupEvent(
+      DownloadsPanel.panel,
+      "hidden"
+    );
+    DownloadsPanel.hidePanel();
+    await hiddenPromise;
+  }
+  if (download?.target.exists) {
+    try {
+      info("Removing test file: " + download.target.path);
+      if (Services.appinfo.OS === "WINNT") {
+        await IOUtils.setPermissions(download.target.path, 0o600);
+      }
+      await IOUtils.remove(download.target.path);
+    } catch (ex) {
+      /* ignore */
+    }
+  }
+  for (let dl of await publicList.getAll()) {
+    await publicList.remove(dl);
+  }
+  BrowserTestUtils.removeTab(loadingTab);
+}
+
+/**
+ * Make sure the downloads panel opens automatically with a new download.
+ */
+add_task(async function test_downloads_panel_opens() {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["browser.download.improvements_to_download_panel", true],
+      ["browser.download.always_ask_before_handling_new_types", false],
+      ["browser.download.alwaysOpenPanel", true],
+    ],
+  });
+  await checkPanelOpens();
+});
+
+add_task(async function test_customizemode_doesnt_wreck_things() {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["browser.download.improvements_to_download_panel", true],
+      ["browser.download.always_ask_before_handling_new_types", false],
+      ["browser.download.alwaysOpenPanel", true],
+    ],
+  });
+
+  // Enter customize mode:
+  let customizationReadyPromise = BrowserTestUtils.waitForEvent(
+    gNavToolbox,
+    "customizationready"
+  );
+  gCustomizeMode.enter();
+  await customizationReadyPromise;
+
+  info("Try to open the panel (will not work, in customize mode)");
+  let promise = promisePanelOpened();
+  DownloadsCommon.getData(window)._notifyDownloadEvent("start");
+  await TestUtils.waitForCondition(
+    () => DownloadsPanel._state == DownloadsPanel.kStateHidden,
+    "Should try to show but stop short and hide the panel"
+  );
+  is(
+    DownloadsPanel._state,
+    DownloadsPanel.kStateHidden,
+    "Should not start opening the panel."
+  );
+
+  let afterCustomizationPromise = BrowserTestUtils.waitForEvent(
+    gNavToolbox,
+    "aftercustomization"
+  );
+  gCustomizeMode.exit();
+  await afterCustomizationPromise;
+
+  // Avoid a failure on Linux where the window isn't active for some reason,
+  // which prevents the window's downloads panel from opening.
+  if (Services.focus.activeWindow != window) {
+    info("Main window is not active, trying to focus.");
+    await SimpleTest.promiseFocus(window);
+    is(Services.focus.activeWindow, window, "Main window should be active.");
+  }
+  DownloadsCommon.getData(window)._notifyDownloadEvent("start");
+  await TestUtils.waitForCondition(
+    () => DownloadsPanel.isPanelShowing,
+    "Panel state should indicate a preparation to be opened"
+  );
+  await promise;
+
+  is(DownloadsPanel.panel.state, "open", "Panel should be opened");
+
+  DownloadsPanel.hidePanel();
+});
+
+/**
+ * Make sure the downloads panel _does not_ open automatically if we set the
+ * pref telling it not to do that.
+ */
+add_task(async function test_downloads_panel_opening_pref() {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["browser.download.improvements_to_download_panel", true],
+      ["browser.download.always_ask_before_handling_new_types", false],
+      ["browser.download.alwaysOpenPanel", false],
+    ],
+  });
+  registerCleanupFunction(async () => {
+    await SpecialPowers.popPrefEnv();
+  });
+  await downloadAndCheckPanel();
+  await SpecialPowers.popPrefEnv();
+});
+
+/**
+ * Make sure the downloads panel _does not_ open automatically if we pass the
+ * parameter telling it not to do that to the download constructor.
+ */
+add_task(async function test_downloads_openDownloadsListOnStart_param() {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["browser.download.improvements_to_download_panel", true],
+      ["browser.download.always_ask_before_handling_new_types", false],
+      ["browser.download.alwaysOpenPanel", true],
+    ],
+  });
+  registerCleanupFunction(async () => {
+    await SpecialPowers.popPrefEnv();
+  });
+  await downloadAndCheckPanel({ openDownloadsListOnStart: false });
+  await SpecialPowers.popPrefEnv();
+});
+
+/**
+ * Make sure the downloads panel _does not_ open automatically when an
+ * extension calls the browser.downloads.download API method while it is
+ * not handling user input, but that we do open it automatically when
+ * the same WebExtensions API is called while handling user input
+ * (See Bug 1759231)
+ */
+add_task(async function test_downloads_panel_on_webext_download_api() {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["browser.download.improvements_to_download_panel", true],
+      ["browser.download.always_ask_before_handling_new_types", false],
+      ["browser.download.alwaysOpenPanel", true],
+    ],
+  });
+  registerCleanupFunction(async () => {
+    await SpecialPowers.popPrefEnv();
+  });
+
+  const extension = ExtensionTestUtils.loadExtension({
+    manifest: {
+      permissions: ["downloads"],
+    },
+    background() {
+      async function startDownload(downloadOptions) {
+        /* globals browser */
+        const downloadId = await browser.downloads.download(downloadOptions);
+        const downloadDone = new Promise(resolve => {
+          browser.downloads.onChanged.addListener(function listener(delta) {
+            browser.test.log(`downloads.onChanged = ${JSON.stringify(delta)}`);
+            if (
+              delta.id == downloadId &&
+              delta.state?.current !== "in_progress"
+            ) {
+              browser.downloads.onChanged.removeListener(listener);
+              resolve();
+            }
+          });
+        });
+
+        browser.test.sendMessage("start-download:done");
+        await downloadDone;
+        await browser.downloads.removeFile(downloadId);
+        browser.test.sendMessage("removed-download-file");
+      }
+
+      browser.test.onMessage.addListener(
+        (msg, { withHandlingUserInput, downloadOptions }) => {
+          if (msg !== "start-download") {
+            browser.test.fail(`Got unexpected test message: ${msg}`);
+            return;
+          }
+
+          if (withHandlingUserInput) {
+            browser.test.withHandlingUserInput(() =>
+              startDownload(downloadOptions)
+            );
+          } else {
+            startDownload(downloadOptions);
+          }
+        }
+      );
+    },
+  });
+
+  await extension.startup();
+
+  startServer();
+
+  async function testExtensionDownloadCall({ withHandlingUserInput }) {
+    mustInterruptResponses();
+    let rnd = Math.random();
+    let url = httpUrl(`interruptible.txt?q=${rnd}`);
+
+    extension.sendMessage("start-download", {
+      withHandlingUserInput,
+      downloadOptions: { url },
+    });
+    await extension.awaitMessage("start-download:done");
+
+    let publicList = await Downloads.getList(Downloads.PUBLIC);
+    let downloads = await publicList.getAll();
+
+    let download = downloads.find(d => d.source.url === url);
+    is(download.source.url, url, "download has the expected url");
+    is(
+      download.openDownloadsListOnStart,
+      withHandlingUserInput,
+      `download panel should ${withHandlingUserInput ? "open" : "stay closed"}`
+    );
+
+    continueResponses();
+    await extension.awaitMessage("removed-download-file");
+  }
+
+  info(
+    "Test extension downloads.download API method call without handling user input"
+  );
+  await testExtensionDownloadCall({ withHandlingUserInput: true });
+
+  info(
+    "Test extension downloads.download API method call while handling user input"
+  );
+  await testExtensionDownloadCall({ withHandlingUserInput: false });
+
+  await extension.unload();
+  await SpecialPowers.popPrefEnv();
+});
+
+/**
+ * Make sure the downloads panel opens automatically with new download, only if
+ * no other downloads are in progress.
+ */
+add_task(async function test_downloads_panel_remains_closed() {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["browser.download.improvements_to_download_panel", true],
+      ["browser.download.always_ask_before_handling_new_types", false],
+    ],
+  });
+  await task_addDownloads([
+    { state: DownloadsCommon.DOWNLOAD_DOWNLOADING },
+    { state: DownloadsCommon.DOWNLOAD_DOWNLOADING },
+  ]);
+
+  let publicList = await Downloads.getList(Downloads.PUBLIC);
+  let downloads = await publicList.getAll();
+
+  info("setting 2 downloads to be in progress");
+  downloads[0].stopped = false;
+  downloads[1].stopped = false;
+
+  let oldShowEventNotification = DownloadsIndicatorView.showEventNotification;
+
+  registerCleanupFunction(async () => {
+    // Remove all downloads created during the test.
+    for (let download of downloads) {
+      await publicList.remove(download);
+    }
+    DownloadsIndicatorView.showEventNotification = oldShowEventNotification;
+  });
+
+  let promiseDownloadStartedNotification = new Promise(resolve => {
+    // Instead of downloads panel opening, download notification should be shown.
+    DownloadsIndicatorView.showEventNotification = aType => {
+      if (aType == "start") {
+        DownloadsIndicatorView.showEventNotification = oldShowEventNotification;
+        resolve();
+      }
+    };
+  });
+
+  DownloadsCommon.getData(window)._notifyDownloadEvent("start");
+
+  is(
+    DownloadsPanel.isPanelShowing,
+    false,
+    "Panel state should NOT indicate a preparation to be opened"
+  );
+
+  await promiseDownloadStartedNotification;
+
+  is(DownloadsPanel.panel.state, "closed", "Panel should be closed");
+
+  for (let download of downloads) {
+    await publicList.remove(download);
+  }
+  is((await publicList.getAll()).length, 0, "Should have no downloads left.");
+});
+
+/**
+ * Make sure the downloads panel doesn't open if the window isn't in the
+ * foreground.
+ */
+add_task(async function test_downloads_panel_inactive_window() {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["browser.download.improvements_to_download_panel", true],
+      ["browser.download.always_ask_before_handling_new_types", false],
+    ],
+  });
+
+  let oldShowEventNotification = DownloadsIndicatorView.showEventNotification;
+
+  registerCleanupFunction(async () => {
+    DownloadsIndicatorView.showEventNotification = oldShowEventNotification;
+  });
+
+  let promiseDownloadStartedNotification = new Promise(resolve => {
+    // Instead of downloads panel opening, download notification should be shown.
+    DownloadsIndicatorView.showEventNotification = aType => {
+      if (aType == "start") {
+        DownloadsIndicatorView.showEventNotification = oldShowEventNotification;
+        resolve();
+      }
+    };
+  });
+
+  let testRunnerWindow = Array.from(Services.wm.getEnumerator("")).find(
+    someWin => someWin != window
+  );
+
+  await SimpleTest.promiseFocus(testRunnerWindow);
+
+  DownloadsCommon.getData(window)._notifyDownloadEvent("start");
+
+  is(
+    DownloadsPanel.isPanelShowing,
+    false,
+    "Panel state should NOT indicate a preparation to be opened"
+  );
+
+  await promiseDownloadStartedNotification;
+  await SimpleTest.promiseFocus(window);
+
+  is(DownloadsPanel.panel.state, "closed", "Panel should be closed");
+
+  testRunnerWindow = null;
+});
+
+/**
+ * When right-clicking the downloads toolbar button, there should be a menuitem
+ * for toggling alwaysOpenPanel. Check that it works correctly.
+ */
+add_task(async function test_alwaysOpenPanel_menuitem() {
+  const alwaysOpenPanelPref = "browser.download.alwaysOpenPanel";
+  let checkbox = document.getElementById(
+    "toolbar-context-always-open-downloads-panel"
+  );
+  let button = document.getElementById("downloads-button");
+
+  Services.prefs.clearUserPref(alwaysOpenPanelPref);
+  await SpecialPowers.pushPrefEnv({
+    set: [["browser.download.autohideButton", false]],
+  });
+  registerCleanupFunction(async () => {
+    await SpecialPowers.popPrefEnv();
+    Services.prefs.clearUserPref(alwaysOpenPanelPref);
+  });
+
+  is(button.hidden, false, "Downloads button should not be hidden.");
+
+  info("Check context menu for downloads button.");
+  await openContextMenu(button);
+  is(checkbox.hidden, false, "Always Open checkbox is visible.");
+  is(checkbox.getAttribute("checked"), "true", "Always Open is enabled.");
+
+  info("Disable Always Open via context menu.");
+  clickCheckbox(checkbox);
+  is(
+    Services.prefs.getBoolPref(alwaysOpenPanelPref),
+    false,
+    "Always Open pref has been set to false."
+  );
+
+  await downloadAndCheckPanel();
+
+  await openContextMenu(button);
+  is(checkbox.hidden, false, "Always Open checkbox is visible.");
+  isnot(checkbox.getAttribute("checked"), "true", "Always Open is disabled.");
+
+  info("Enable Always Open via context menu");
+  clickCheckbox(checkbox);
+  is(
+    Services.prefs.getBoolPref(alwaysOpenPanelPref),
+    true,
+    "Pref has been set to true"
+  );
+
+  await checkPanelOpens();
+});
+
+/**
+ * Verify that the downloads panel opens if the download did not open a file
+ * picker or UCT dialog
+ */
+add_task(async function test_downloads_panel_after_no_dialogs() {
+  await testDownloadsPanelAfterDialog({ expectPanelToOpen: true });
+  ok(true, "Downloads panel opened because no dialogs were opened.");
+});
+
+/**
+ * Verify that the downloads panel doesn't open if the download opened an
+ * unknown content type dialog (e.g. action = always ask)
+ */
+add_task(async function test_downloads_panel_after_UCT_dialog() {
+  await testDownloadsPanelAfterDialog({
+    expectPanelToOpen: false,
+    preferredAction: Ci.nsIHandlerInfo.alwaysAsk,
+  });
+  ok(true, "Downloads panel suppressed after UCT dialog.");
+});
+
+/**
+ * Verify that the downloads panel doesn't open if the download opened a file
+ * picker dialog (e.g. useDownloadDir = false)
+ */
+add_task(async function test_downloads_panel_after_file_picker_dialog() {
+  await testDownloadsPanelAfterDialog({
+    expectPanelToOpen: false,
+    preferredAction: Ci.nsIHandlerInfo.saveToDisk,
+    askWhereToSave: true,
+  });
+  ok(true, "Downloads panel suppressed after file picker dialog.");
+});
+
+/**
+ * Verify that the downloads panel doesn't open if the download opened both
+ * dialogs (e.g. default action = always ask AND useDownloadDir = false)
+ */
+add_task(async function test_downloads_panel_after_both_dialogs() {
+  await testDownloadsPanelAfterDialog({
+    expectPanelToOpen: false,
+    preferredAction: Ci.nsIHandlerInfo.alwaysAsk,
+    askWhereToSave: true,
+  });
+  ok(true, "Downloads panel suppressed after UCT and file picker dialogs.");
+});
diff --git a/browser/components/downloads/test/browser/browser_downloads_pauseResume.js b/browser/components/downloads/test/browser/browser_downloads_pauseResume.js
new file mode 100644
index 0000000000..0fddff6a16
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_downloads_pauseResume.js
@@ -0,0 +1,49 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+registerCleanupFunction(async function() {
+  await task_resetState();
+});
+
+add_task(async function test_downloads_library() {
+  let DownloadData = [];
+  for (let i = 0; i < 20; i++) {
+    DownloadData.push({ state: DownloadsCommon.DOWNLOAD_PAUSED });
+  }
+
+  // Ensure that state is reset in case previous tests didn't finish.
+  await task_resetState();
+
+  // Populate the downloads database with the data required by this test.
+  await task_addDownloads(DownloadData);
+
+  let win = await openLibrary("Downloads");
+  registerCleanupFunction(function() {
+    win.close();
+  });
+
+  let listbox = win.document.getElementById("downloadsListBox");
+  ok(listbox, "Download list box present");
+
+  // Select one of the downloads.
+  listbox.itemChildren[0].click();
+  listbox.itemChildren[0]._shell._download.hasPartialData = true;
+
+  EventUtils.synthesizeKey(" ", {}, win);
+  is(
+    listbox.itemChildren[0]._shell._downloadState,
+    DownloadsCommon.DOWNLOAD_DOWNLOADING,
+    "Download state toggled from paused to downloading"
+  );
+
+  // there is no event to wait for in some cases, we need to wait for the keypress to potentially propagate
+  // eslint-disable-next-line mozilla/no-arbitrary-setTimeout
+  await new Promise(r => setTimeout(r, 500));
+  is(
+    listbox.scrollTop,
+    0,
+    "All downloads view did not scroll when spacebar event fired on a selected download"
+  );
+});
diff --git a/browser/components/downloads/test/browser/browser_first_download_panel.js b/browser/components/downloads/test/browser/browser_first_download_panel.js
new file mode 100644
index 0000000000..488f98ecc0
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_first_download_panel.js
@@ -0,0 +1,74 @@
+/* -*- indent-tabs-mode: nil; js-indent-level: 2 -*- */
+/* vim: set ts=2 et sw=2 tw=80: */
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+/* eslint-disable mozilla/no-arbitrary-setTimeout */
+
+/**
+ * Make sure the downloads panel only opens automatically on the first
+ * download it notices. All subsequent downloads, even across sessions, should
+ * not open the panel automatically.
+ */
+add_task(async function test_first_download_panel() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["browser.download.autohideButton", false]],
+  });
+  await promiseButtonShown("downloads-button");
+  // Clear the download panel has shown preference first as this test is used to
+  // verify this preference's behaviour.
+  let oldPrefValue = Services.prefs.getBoolPref("browser.download.panel.shown");
+  Services.prefs.setBoolPref("browser.download.panel.shown", false);
+
+  registerCleanupFunction(async function() {
+    // Clean up when the test finishes.
+    await task_resetState();
+
+    // Set the preference instead of clearing it afterwards to ensure the
+    // right value is used no matter what the default was. This ensures the
+    // panel doesn't appear and affect other tests.
+    Services.prefs.setBoolPref("browser.download.panel.shown", oldPrefValue);
+  });
+
+  // Ensure that state is reset in case previous tests didn't finish.
+  await task_resetState();
+
+  // With this set to false, we should automatically open the panel the first
+  // time a download is started.
+  DownloadsCommon.getData(window).panelHasShownBefore = false;
+
+  info("waiting for panel open");
+  let promise = promisePanelOpened();
+  DownloadsCommon.getData(window)._notifyDownloadEvent("start");
+  await promise;
+
+  // If we got here, that means the panel opened.
+  DownloadsPanel.hidePanel();
+
+  ok(
+    DownloadsCommon.getData(window).panelHasShownBefore,
+    "Should have recorded that the panel was opened on a download."
+  );
+
+  // If browser.download.improvements_to_download_panel is enabled, this will fail
+  // because we always open a downloads panel as long as there is no other simulatenous
+  // download. So, first ensure that this pref is already false.
+  if (
+    !SpecialPowers.getBoolPref(
+      "browser.download.improvements_to_download_panel"
+    )
+  ) {
+    // Next, make sure that if we start another download, we don't open the
+    // panel automatically.
+    let originalOnPopupShown = DownloadsPanel.onPopupShown;
+    DownloadsPanel.onPopupShown = function() {
+      originalOnPopupShown.apply(this, arguments);
+      ok(false, "Should not have opened the downloads panel.");
+    };
+
+    DownloadsCommon.getData(window)._notifyDownloadEvent("start");
+
+    // Wait 2 seconds to ensure that the panel does not open.
+    await new Promise(resolve => setTimeout(resolve, 2000));
+    DownloadsPanel.onPopupShown = originalOnPopupShown;
+  }
+});
diff --git a/browser/components/downloads/test/browser/browser_go_to_download_page.js b/browser/components/downloads/test/browser/browser_go_to_download_page.js
new file mode 100644
index 0000000000..3d1eda2e4d
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_go_to_download_page.js
@@ -0,0 +1,93 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+const ReferrerInfo = Components.Constructor(
+  "@mozilla.org/referrer-info;1",
+  "nsIReferrerInfo",
+  "init"
+);
+
+const TEST_REFERRER = "https://example.com/";
+
+registerCleanupFunction(async function() {
+  await task_resetState();
+  await PlacesUtils.history.clear();
+});
+
+async function addDownload(referrerInfo) {
+  let startTimeMs = Date.now();
+
+  let publicList = await Downloads.getList(Downloads.PUBLIC);
+  let downloadData = {
+    source: {
+      url: "http://www.example.com/test-download.txt",
+      referrerInfo,
+    },
+    target: {
+      path: gTestTargetFile.path,
+    },
+    startTime: new Date(startTimeMs++),
+  };
+  let download = await Downloads.createDownload(downloadData);
+  await publicList.add(download);
+  await download.start();
+}
+
+/**
+ * Make sure "Go To Download Page" is enabled and works as expected.
+ */
+add_task(async function test_go_to_download_page() {
+  let referrerInfo = new ReferrerInfo(
+    Ci.nsIReferrerInfo.NO_REFERRER,
+    true,
+    NetUtil.newURI(TEST_REFERRER)
+  );
+
+  let tabPromise = BrowserTestUtils.waitForNewTab(gBrowser, TEST_REFERRER);
+
+  // Wait for focus first
+  await promiseFocus();
+
+  // Ensure that state is reset in case previous tests didn't finish.
+  await task_resetState();
+
+  // Populate the downloads database with the data required by this test.
+  await addDownload(referrerInfo);
+
+  // Open the user interface and wait for data to be fully loaded.
+  await task_openPanel();
+
+  let win = await openLibrary("Downloads");
+  registerCleanupFunction(function() {
+    win.close();
+  });
+
+  let listbox = win.document.getElementById("downloadsListBox");
+  ok(listbox, "download list box present");
+
+  // Select one of the downloads.
+  listbox.itemChildren[0].click();
+
+  let contextMenu = win.document.getElementById("downloadsContextMenu");
+
+  let popupShownPromise = BrowserTestUtils.waitForEvent(
+    contextMenu,
+    "popupshown"
+  );
+  EventUtils.synthesizeMouseAtCenter(
+    listbox.itemChildren[0],
+    { type: "contextmenu", button: 2 },
+    win
+  );
+  await popupShownPromise;
+
+  // Find and click "Go To Download Page"
+  let goToDownloadButton = [...contextMenu.children].find(
+    child => child.command == "downloadsCmd_openReferrer"
+  );
+  contextMenu.activateItem(goToDownloadButton);
+
+  let newTab = await tabPromise;
+  ok(newTab, "Go To Download Page opened a new tab");
+  gBrowser.removeTab(newTab);
+});
diff --git a/browser/components/downloads/test/browser/browser_iframe_gone_mid_download.js b/browser/components/downloads/test/browser/browser_iframe_gone_mid_download.js
new file mode 100644
index 0000000000..77a8a987fe
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_iframe_gone_mid_download.js
@@ -0,0 +1,76 @@
+const SAVE_PER_SITE_PREF = "browser.download.lastDir.savePerSite";
+
+function test_deleted_iframe(perSitePref, windowOptions = {}) {
+  return async function() {
+    await SpecialPowers.pushPrefEnv({
+      set: [[SAVE_PER_SITE_PREF, perSitePref]],
+    });
+    let { DownloadLastDir } = ChromeUtils.import(
+      "resource://gre/modules/DownloadLastDir.jsm"
+    );
+
+    let win = await BrowserTestUtils.openNewBrowserWindow(windowOptions);
+    let tab = await BrowserTestUtils.openNewForegroundTab(
+      win.gBrowser,
+      "about:mozilla"
+    );
+
+    let doc = tab.linkedBrowser.contentDocument;
+    let iframe = doc.createElement("iframe");
+    doc.body.appendChild(iframe);
+
+    ok(iframe.contentWindow, "iframe should have a window");
+    let gDownloadLastDir = new DownloadLastDir(iframe.contentWindow);
+    let cw = iframe.contentWindow;
+    let promiseIframeWindowGone = new Promise((resolve, reject) => {
+      Services.obs.addObserver(function obs(subject, topic) {
+        if (subject == cw) {
+          Services.obs.removeObserver(obs, topic);
+          resolve();
+        }
+      }, "dom-window-destroyed");
+    });
+    iframe.remove();
+    await promiseIframeWindowGone;
+    cw = null;
+    ok(!iframe.contentWindow, "Managed to destroy iframe");
+
+    let someDir = "blah";
+    try {
+      someDir = await new Promise((resolve, reject) => {
+        gDownloadLastDir.getFileAsync("http://www.mozilla.org/", function(dir) {
+          resolve(dir);
+        });
+      });
+    } catch (ex) {
+      ok(
+        false,
+        "Got an exception trying to get the directory where things should be saved."
+      );
+      console.error(ex);
+    }
+    // NB: someDir can legitimately be null here when set, hence the 'blah' workaround:
+    isnot(
+      someDir,
+      "blah",
+      "Should get a file even after the window was destroyed."
+    );
+
+    try {
+      gDownloadLastDir.setFile("http://www.mozilla.org/", null);
+    } catch (ex) {
+      ok(
+        false,
+        "Got an exception trying to set the directory where things should be saved."
+      );
+      console.error(ex);
+    }
+
+    await BrowserTestUtils.closeWindow(win);
+  };
+}
+
+add_task(test_deleted_iframe(false));
+add_task(test_deleted_iframe(false));
+add_task(test_deleted_iframe(true, { private: true }));
+add_task(test_deleted_iframe(true, { private: true }));
diff --git a/browser/components/downloads/test/browser/browser_image_mimetype_issues.js b/browser/components/downloads/test/browser/browser_image_mimetype_issues.js
new file mode 100644
index 0000000000..16c9f31e7b
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_image_mimetype_issues.js
@@ -0,0 +1,136 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const TEST_ROOT = getRootDirectory(gTestPath).replace(
+  "chrome://mochitests/content",
+  "http://example.com"
+);
+
+var MockFilePicker = SpecialPowers.MockFilePicker;
+MockFilePicker.init(window);
+
+/*
+ * Popular websites implement image optimization as serving files with
+ * extension ".jpg" but content type "image/webp". If we save such images,
+ * we should actually save them with a .webp extension as that is what
+ * they are.
+ */
+
+/**
+ * Test the above with the "save image as" context menu.
+ */
+add_task(async function test_save_image_webp_with_jpeg_extension() {
+  await BrowserTestUtils.withNewTab(
+    `data:text/html,<img src="${TEST_ROOT}/not-really-a-jpeg.jpeg?convert=webp">`,
+    async browser => {
+      let menu = document.getElementById("contentAreaContextMenu");
+      let popupShown = BrowserTestUtils.waitForEvent(menu, "popupshown");
+      BrowserTestUtils.synthesizeMouse(
+        "img",
+        5,
+        5,
+        { type: "contextmenu", button: 2 },
+        browser
+      );
+      await popupShown;
+
+      await new Promise(resolve => {
+        MockFilePicker.showCallback = function(fp) {
+          ok(
+            fp.defaultString.endsWith("webp"),
+            `filepicker for image has "${fp.defaultString}", should end in webp`
+          );
+          setTimeout(resolve, 0);
+          return Ci.nsIFilePicker.returnCancel;
+        };
+        let menuitem = menu.querySelector("#context-saveimage");
+        menu.activateItem(menuitem);
+      });
+    }
+  );
+});
+
+/**
+ * Test with the "save link as" context menu.
+ */
+add_task(async function test_save_link_webp_with_jpeg_extension() {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["browser.download.improvements_to_download_panel", true],
+      ["browser.download.always_ask_before_handling_new_types", false],
+      ["browser.download.useDownloadDir", false],
+    ],
+  });
+  await BrowserTestUtils.withNewTab(
+    `data:text/html,<a href="${TEST_ROOT}/not-really-a-jpeg.jpeg?convert=webp">Nice image</a>`,
+    async browser => {
+      let menu = document.getElementById("contentAreaContextMenu");
+      let popupShown = BrowserTestUtils.waitForEvent(menu, "popupshown");
+      BrowserTestUtils.synthesizeMouse(
+        "a[href]",
+        5,
+        5,
+        { type: "contextmenu", button: 2 },
+        browser
+      );
+      await popupShown;
+
+      await new Promise(resolve => {
+        MockFilePicker.showCallback = function(fp) {
+          ok(
+            fp.defaultString.endsWith("webp"),
+            `filepicker for link has "${fp.defaultString}", should end in webp`
+          );
+          setTimeout(resolve, 0);
+          return Ci.nsIFilePicker.returnCancel;
+        };
+        let menuitem = menu.querySelector("#context-savelink");
+        menu.activateItem(menuitem);
+      });
+    }
+  );
+});
+
+/**
+ * Test with the main "save page" command.
+ */
+add_task(async function test_save_page_on_image_document() {
+  await BrowserTestUtils.withNewTab(
+    `${TEST_ROOT}/not-really-a-jpeg.jpeg?convert=webp`,
+    async browser => {
+      await new Promise(resolve => {
+        MockFilePicker.showCallback = function(fp) {
+          ok(
+            fp.defaultString.endsWith("webp"),
+            `filepicker for "save page" has "${fp.defaultString}", should end in webp`
+          );
+          setTimeout(resolve, 0);
+          return Ci.nsIFilePicker.returnCancel;
+        };
+        document.getElementById("Browser:SavePage").doCommand();
+      });
+    }
+  );
+});
+
+/**
+ * Make sure that a valid JPEG image using the .JPG extension doesn't
+ * get it replaced with .jpeg.
+ */
+add_task(async function test_save_page_on_JPEG_image_document() {
+  await BrowserTestUtils.withNewTab(`${TEST_ROOT}/blank.JPG`, async browser => {
+    await new Promise(resolve => {
+      MockFilePicker.showCallback = function(fp) {
+        ok(
+          fp.defaultString.endsWith("JPG"),
+          `filepicker for "save page" has "${fp.defaultString}", should end in JPG`
+        );
+        setTimeout(resolve, 0);
+        return Ci.nsIFilePicker.returnCancel;
+      };
+      document.getElementById("Browser:SavePage").doCommand();
+    });
+  });
+});
diff --git a/browser/components/downloads/test/browser/browser_indicatorDrop.js b/browser/components/downloads/test/browser/browser_indicatorDrop.js
new file mode 100644
index 0000000000..1cbdd89761
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_indicatorDrop.js
@@ -0,0 +1,38 @@
+/* -*- indent-tabs-mode: nil; js-indent-level: 2 -*- */
+/* vim: set ts=2 et sw=2 tw=80: */
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+registerCleanupFunction(async function() {
+  await task_resetState();
+  await PlacesUtils.history.clear();
+});
+
+add_task(async function test_indicatorDrop() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["browser.download.autohideButton", false]],
+  });
+  let downloadButton = document.getElementById("downloads-button");
+  ok(downloadButton, "download button present");
+  await promiseButtonShown(downloadButton.id);
+
+  let EventUtils = {};
+  Services.scriptloader.loadSubScript(
+    "chrome://mochikit/content/tests/SimpleTest/EventUtils.js",
+    EventUtils
+  );
+
+  // Ensure that state is reset in case previous tests didn't finish.
+  await task_resetState();
+
+  await setDownloadDir();
+
+  startServer();
+
+  await simulateDropAndCheck(window, downloadButton, [httpUrl("file1.txt")]);
+  await simulateDropAndCheck(window, downloadButton, [
+    httpUrl("file1.txt"),
+    httpUrl("file2.txt"),
+    httpUrl("file3.txt"),
+  ]);
+});
diff --git a/browser/components/downloads/test/browser/browser_libraryDrop.js b/browser/components/downloads/test/browser/browser_libraryDrop.js
new file mode 100644
index 0000000000..629b0ab834
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_libraryDrop.js
@@ -0,0 +1,39 @@
+/* -*- indent-tabs-mode: nil; js-indent-level: 2 -*- */
+/* vim: set ts=2 et sw=2 tw=80: */
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+registerCleanupFunction(async function() {
+  await task_resetState();
+  await PlacesUtils.history.clear();
+});
+
+add_task(async function test_indicatorDrop() {
+  let EventUtils = {};
+  Services.scriptloader.loadSubScript(
+    "chrome://mochikit/content/tests/SimpleTest/EventUtils.js",
+    EventUtils
+  );
+
+  // Ensure that state is reset in case previous tests didn't finish.
+  await task_resetState();
+
+  await setDownloadDir();
+
+  startServer();
+
+  let win = await openLibrary("Downloads");
+  registerCleanupFunction(function() {
+    win.close();
+  });
+
+  let listBox = win.document.getElementById("downloadsListBox");
+  ok(listBox, "download list box present");
+
+  await simulateDropAndCheck(win, listBox, [httpUrl("file1.txt")]);
+  await simulateDropAndCheck(win, listBox, [
+    httpUrl("file1.txt"),
+    httpUrl("file2.txt"),
+    httpUrl("file3.txt"),
+  ]);
+});
diff --git a/browser/components/downloads/test/browser/browser_library_clearall.js b/browser/components/downloads/test/browser/browser_library_clearall.js
new file mode 100644
index 0000000000..81aca9d47a
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_library_clearall.js
@@ -0,0 +1,123 @@
+/* -*- indent-tabs-mode: nil; js-indent-level: 2 -*- */
+/* vim: set ts=2 et sw=2 tw=80: */
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+ChromeUtils.defineESModuleGetters(this, {
+  PlacesTestUtils: "resource://testing-common/PlacesTestUtils.sys.mjs",
+});
+
+let win;
+
+function waitForChildren(element, callback) {
+  let MutationObserver = element.ownerGlobal.MutationObserver;
+  return new Promise(resolve => {
+    let observer = new MutationObserver(() => {
+      if (callback()) {
+        observer.disconnect();
+        resolve();
+      }
+    });
+    observer.observe(element, { childList: true });
+  });
+}
+
+async function waitForChildrenLength(element, length, callback) {
+  if (element.childElementCount != length) {
+    await waitForChildren(element, () => element.childElementCount == length);
+  }
+}
+
+registerCleanupFunction(async function() {
+  await task_resetState();
+  await PlacesUtils.history.clear();
+});
+
+async function testClearingDownloads(clearCallback) {
+  const DOWNLOAD_DATA = [
+    httpUrl("file1.txt"),
+    httpUrl("file2.txt"),
+    httpUrl("file3.txt"),
+  ];
+
+  let listbox = win.document.getElementById("downloadsListBox");
+  ok(listbox, "download list box present");
+
+  let promiseLength = waitForChildrenLength(listbox, DOWNLOAD_DATA.length);
+  await simulateDropAndCheck(win, listbox, DOWNLOAD_DATA);
+  await promiseLength;
+
+  let receivedNotifications = [];
+  const promiseNotification = PlacesTestUtils.waitForNotification(
+    "page-removed",
+    events => {
+      for (const { url, isRemovedFromStore } of events) {
+        Assert.ok(isRemovedFromStore);
+
+        if (DOWNLOAD_DATA.includes(url)) {
+          receivedNotifications.push(url);
+        }
+      }
+      return receivedNotifications.length == DOWNLOAD_DATA.length;
+    },
+    "places"
+  );
+
+  promiseLength = waitForChildrenLength(listbox, 0);
+  await clearCallback(listbox);
+  await promiseLength;
+
+  await promiseNotification;
+
+  Assert.deepEqual(
+    receivedNotifications.sort(),
+    DOWNLOAD_DATA.sort(),
+    "Should have received notifications for each URL"
+  );
+}
+
+add_setup(async function() {
+  // Ensure that state is reset in case previous tests didn't finish.
+  await task_resetState();
+
+  await setDownloadDir();
+
+  startServer();
+
+  win = await openLibrary("Downloads");
+  registerCleanupFunction(function() {
+    win.close();
+  });
+});
+
+add_task(async function test_clear_downloads_toolbar() {
+  await testClearingDownloads(async () => {
+    win.document.getElementById("clearDownloadsButton").click();
+  });
+});
+
+add_task(async function test_clear_downloads_context_menu() {
+  await testClearingDownloads(async listbox => {
+    // Select one of the downloads.
+    listbox.itemChildren[0].click();
+
+    let contextMenu = win.document.getElementById("downloadsContextMenu");
+
+    let popupShownPromise = BrowserTestUtils.waitForEvent(
+      contextMenu,
+      "popupshown"
+    );
+    EventUtils.synthesizeMouseAtCenter(
+      listbox.itemChildren[0],
+      { type: "contextmenu", button: 2 },
+      win
+    );
+    await popupShownPromise;
+
+    // Find the clear context item.
+    let clearDownloadsButton = [...contextMenu.children].find(
+      child => child.command == "downloadsCmd_clearDownloads"
+    );
+    contextMenu.activateItem(clearDownloadsButton);
+  });
+});
diff --git a/browser/components/downloads/test/browser/browser_library_select_all.js b/browser/components/downloads/test/browser/browser_library_select_all.js
new file mode 100644
index 0000000000..9944909bc5
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_library_select_all.js
@@ -0,0 +1,77 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+let gDownloadDir;
+
+add_setup(async function() {
+  await task_resetState();
+
+  if (!gDownloadDir) {
+    gDownloadDir = await setDownloadDir();
+  }
+
+  await task_addDownloads([
+    {
+      state: DownloadsCommon.DOWNLOAD_FINISHED,
+      target: await createDownloadedFile(
+        PathUtils.join(gDownloadDir, "downloaded_one.txt"),
+        "Test file 1"
+      ),
+    },
+    {
+      state: DownloadsCommon.DOWNLOAD_FINISHED,
+      target: await createDownloadedFile(
+        PathUtils.join(gDownloadDir, "downloaded_two.txt"),
+        "Test file 2"
+      ),
+    },
+  ]);
+  registerCleanupFunction(async function() {
+    await task_resetState();
+    await PlacesUtils.history.clear();
+  });
+});
+
+add_task(async function test_select_all() {
+  let win = await openLibrary("Downloads");
+  registerCleanupFunction(() => {
+    win.close();
+  });
+
+  let listbox = win.document.getElementById("downloadsListBox");
+  Assert.ok(listbox, "download list box present");
+  listbox.focus();
+  await TestUtils.waitForCondition(
+    () => listbox.children.length == 2 && listbox.selectedItems.length == 1,
+    "waiting for both items to be present with one selected"
+  );
+  info("Select all the downloads");
+  win.goDoCommand("cmd_selectAll");
+  Assert.equal(
+    listbox.selectedItems.length,
+    listbox.children.length,
+    "All the items should be selected"
+  );
+
+  info("Search for a specific download");
+  let searchBox = win.document.getElementById("searchFilter");
+  searchBox.value = "_one";
+  win.PlacesSearchBox.search(searchBox.value);
+  await TestUtils.waitForCondition(() => {
+    let visibleItems = Array.from(listbox.children).filter(c => !c.hidden);
+    return (
+      visibleItems.length == 1 &&
+      visibleItems[0]._shell.download.target.path.includes("_one")
+    );
+  }, "Waiting for the search to complete");
+  Assert.equal(
+    listbox.selectedItems.length,
+    0,
+    "Check previous selection has been cleared by the search"
+  );
+  info("Select all the downloads");
+  win.goDoCommand("cmd_selectAll");
+  Assert.equal(listbox.children.length, 2, "Both items are present");
+  Assert.equal(listbox.selectedItems.length, 1, "Only one item is selected");
+  Assert.ok(!listbox.selectedItem.hidden, "The selected item is not hidden");
+});
diff --git a/browser/components/downloads/test/browser/browser_overflow_anchor.js b/browser/components/downloads/test/browser/browser_overflow_anchor.js
new file mode 100644
index 0000000000..e02ed81157
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_overflow_anchor.js
@@ -0,0 +1,59 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+registerCleanupFunction(async function() {
+  // Clean up when the test finishes.
+  await task_resetState();
+});
+
+/**
+ * Make sure the downloads button and indicator overflows into the nav-bar
+ * chevron properly, and then when those buttons are clicked in the overflow
+ * panel that the downloads panel anchors to the chevron`s icon.
+ */
+add_task(async function test_overflow_anchor() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["browser.download.autohideButton", false]],
+  });
+  // Ensure that state is reset in case previous tests didn't finish.
+  await task_resetState();
+
+  // The downloads button should not be overflowed to begin with.
+  let button = CustomizableUI.getWidget("downloads-button").forWindow(window);
+  ok(!button.overflowed, "Downloads button should not be overflowed.");
+  is(
+    button.node.getAttribute("cui-areatype"),
+    "toolbar",
+    "Button should know it's in the toolbar"
+  );
+
+  await gCustomizeMode.addToPanel(button.node);
+
+  let promise = promisePanelOpened();
+  EventUtils.sendMouseEvent({ type: "mousedown", button: 0 }, button.node);
+  info("waiting for panel to open");
+  await promise;
+
+  let panel = DownloadsPanel.panel;
+  let chevron = document.getElementById("nav-bar-overflow-button");
+
+  is(
+    panel.anchorNode,
+    chevron.icon,
+    "Panel should be anchored to the chevron`s icon."
+  );
+
+  DownloadsPanel.hidePanel();
+
+  gCustomizeMode.addToToolbar(button.node);
+
+  // Now try opening the panel again.
+  promise = promisePanelOpened();
+  EventUtils.sendMouseEvent({ type: "mousedown", button: 0 }, button.node);
+  await promise;
+
+  let downloadsAnchor = button.node.badgeStack;
+  is(panel.anchorNode, downloadsAnchor);
+
+  DownloadsPanel.hidePanel();
+});
diff --git a/browser/components/downloads/test/browser/browser_pdfjs_preview.js b/browser/components/downloads/test/browser/browser_pdfjs_preview.js
new file mode 100644
index 0000000000..3930db8923
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_pdfjs_preview.js
@@ -0,0 +1,753 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+let gDownloadDir;
+
+// The test is long, and it's not worth splitting it since all the tests share
+// the same boilerplate code.
+requestLongerTimeout(4);
+
+SimpleTest.requestFlakyTimeout(
+  "Giving a chance for possible last-pb-context-exited to occur (Bug 1329912)"
+);
+
+/*
+  Coverage for opening downloaded PDFs from download views
+*/
+
+const TestCases = [
+  {
+    name: "Download panel, default click behavior",
+    whichUI: "downloadPanel",
+    itemSelector: "#downloadsListBox richlistitem .downloadMainArea",
+    async userEvents(itemTarget, win) {
+      EventUtils.synthesizeMouseAtCenter(itemTarget, {}, win);
+    },
+    expected: {
+      downloadCount: 1,
+      newWindow: false,
+      opensTab: true,
+      tabSelected: true,
+    },
+  },
+  {
+    name: "Download panel, system viewer menu items prefd off",
+    whichUI: "downloadPanel",
+    itemSelector: "#downloadsListBox richlistitem .downloadMainArea",
+    async userEvents(itemTarget, win) {
+      EventUtils.synthesizeMouseAtCenter(itemTarget, {}, win);
+    },
+    prefs: [
+      ["browser.download.openInSystemViewerContextMenuItem", false],
+      ["browser.download.alwaysOpenInSystemViewerContextMenuItem", false],
+    ],
+    expected: {
+      downloadCount: 1,
+      newWindow: false,
+      opensTab: true,
+      tabSelected: true,
+      useSystemMenuItemDisabled: true,
+      alwaysMenuItemDisabled: true,
+    },
+  },
+  {
+    name: "Download panel, open from keyboard",
+    whichUI: "downloadPanel",
+    itemSelector: "#downloadsListBox richlistitem .downloadMainArea",
+    async userEvents(itemTarget, win) {
+      itemTarget.focus();
+      EventUtils.synthesizeKey("VK_RETURN", {}, win);
+    },
+    expected: {
+      downloadCount: 1,
+      newWindow: false,
+      opensTab: true,
+      tabSelected: true,
+    },
+  },
+  {
+    name: "Download panel, open in new window",
+    whichUI: "downloadPanel",
+    itemSelector: "#downloadsListBox richlistitem .downloadMainArea",
+    async userEvents(itemTarget, win) {
+      EventUtils.synthesizeMouseAtCenter(itemTarget, { shiftKey: true }, win);
+    },
+    expected: {
+      downloadCount: 1,
+      newWindow: true,
+      opensTab: false,
+      tabSelected: true,
+    },
+  },
+  {
+    name: "Download panel, open foreground tab", // duplicates the default behavior
+    whichUI: "downloadPanel",
+    itemSelector: "#downloadsListBox richlistitem .downloadMainArea",
+    async userEvents(itemTarget, win) {
+      EventUtils.synthesizeMouseAtCenter(
+        itemTarget,
+        { ctrlKey: true, metaKey: true },
+        win
+      );
+    },
+    expected: {
+      downloadCount: 1,
+      newWindow: false,
+      opensTab: true,
+      tabSelected: true,
+    },
+  },
+  {
+    name: "Download panel, open background tab",
+    whichUI: "downloadPanel",
+    itemSelector: "#downloadsListBox richlistitem .downloadMainArea",
+    async userEvents(itemTarget, win) {
+      EventUtils.synthesizeMouseAtCenter(
+        itemTarget,
+        { ctrlKey: true, metaKey: true, shiftKey: true },
+        win
+      );
+    },
+    expected: {
+      downloadCount: 1,
+      newWindow: false,
+      opensTab: true,
+      tabSelected: false,
+    },
+  },
+
+  {
+    name: "Library all downloads dialog, default click behavior",
+    whichUI: "allDownloads",
+    async userEvents(itemTarget, win) {
+      // double click
+      await triggerDblclickOn(itemTarget, {}, win);
+    },
+    expected: {
+      downloadCount: 1,
+      newWindow: false,
+      opensTab: true,
+      tabSelected: true,
+    },
+  },
+  {
+    name: "Library all downloads dialog, system viewer menu items prefd off",
+    whichUI: "allDownloads",
+    async userEvents(itemTarget, win) {
+      // double click
+      await triggerDblclickOn(itemTarget, {}, win);
+    },
+    prefs: [
+      ["browser.download.openInSystemViewerContextMenuItem", false],
+      ["browser.download.alwaysOpenInSystemViewerContextMenuItem", false],
+    ],
+    expected: {
+      downloadCount: 1,
+      newWindow: false,
+      opensTab: true,
+      tabSelected: true,
+      useSystemMenuItemDisabled: true,
+      alwaysMenuItemDisabled: true,
+    },
+  },
+  {
+    name: "Library all downloads dialog, open from keyboard",
+    whichUI: "allDownloads",
+    async userEvents(itemTarget, win) {
+      itemTarget.focus();
+      EventUtils.synthesizeKey("VK_RETURN", {}, win);
+    },
+    expected: {
+      downloadCount: 1,
+      newWindow: false,
+      opensTab: true,
+      tabSelected: true,
+    },
+  },
+  {
+    name: "Library all downloads dialog, open in new window",
+    whichUI: "allDownloads",
+    async userEvents(itemTarget, win) {
+      // double click
+      await triggerDblclickOn(itemTarget, { shiftKey: true }, win);
+    },
+    expected: {
+      downloadCount: 1,
+      newWindow: true,
+      opensTab: false,
+      tabSelected: true,
+    },
+  },
+  {
+    name: "Library all downloads dialog, open foreground tab", // duplicates default behavior
+    whichUI: "allDownloads",
+    async userEvents(itemTarget, win) {
+      // double click
+      await triggerDblclickOn(
+        itemTarget,
+        { ctrlKey: true, metaKey: true },
+        win
+      );
+    },
+    expected: {
+      downloadCount: 1,
+      newWindow: false,
+      opensTab: true,
+      tabSelected: true,
+    },
+  },
+  {
+    name: "Library all downloads dialog, open background tab",
+    whichUI: "allDownloads",
+    async userEvents(itemTarget, win) {
+      // double click
+      await triggerDblclickOn(
+        itemTarget,
+        { ctrlKey: true, metaKey: true, shiftKey: true },
+        win
+      );
+    },
+    expected: {
+      downloadCount: 1,
+      newWindow: false,
+      opensTab: true,
+      tabSelected: false,
+    },
+  },
+  {
+    name: "about:downloads, default click behavior",
+    whichUI: "aboutDownloads",
+    itemSelector: "#downloadsListBox richlistitem .downloadContainer",
+    async userEvents(itemSelector, win) {
+      let browser = win.gBrowser.selectedBrowser;
+      is(browser.currentURI.spec, "about:downloads");
+      await contentTriggerDblclickOn(itemSelector, {}, browser);
+    },
+    expected: {
+      downloadCount: 1,
+      newWindow: false,
+      opensTab: true,
+      tabSelected: true,
+    },
+  },
+  {
+    name: "about:downloads, system viewer menu items prefd off",
+    whichUI: "aboutDownloads",
+    itemSelector: "#downloadsListBox richlistitem .downloadContainer",
+    async userEvents(itemSelector, win) {
+      let browser = win.gBrowser.selectedBrowser;
+      is(browser.currentURI.spec, "about:downloads");
+      await contentTriggerDblclickOn(itemSelector, {}, browser);
+    },
+    prefs: [
+      ["browser.download.openInSystemViewerContextMenuItem", false],
+      ["browser.download.alwaysOpenInSystemViewerContextMenuItem", false],
+    ],
+    expected: {
+      downloadCount: 1,
+      newWindow: false,
+      opensTab: true,
+      tabSelected: true,
+      useSystemMenuItemDisabled: true,
+      alwaysMenuItemDisabled: true,
+    },
+  },
+  {
+    name: "about:downloads, open in new window",
+    whichUI: "aboutDownloads",
+    itemSelector: "#downloadsListBox richlistitem .downloadContainer",
+    async userEvents(itemSelector, win) {
+      let browser = win.gBrowser.selectedBrowser;
+      is(browser.currentURI.spec, "about:downloads");
+      await contentTriggerDblclickOn(itemSelector, { shiftKey: true }, browser);
+    },
+    expected: {
+      downloadCount: 1,
+      newWindow: true,
+      opensTab: false,
+      tabSelected: true,
+    },
+  },
+  {
+    name: "about:downloads, open in foreground tab",
+    whichUI: "aboutDownloads",
+    itemSelector: "#downloadsListBox richlistitem .downloadContainer",
+    async userEvents(itemSelector, win) {
+      let browser = win.gBrowser.selectedBrowser;
+      is(browser.currentURI.spec, "about:downloads");
+      await contentTriggerDblclickOn(
+        itemSelector,
+        { ctrlKey: true, metaKey: true },
+        browser
+      );
+    },
+    expected: {
+      downloadCount: 1,
+      newWindow: false,
+      opensTab: true,
+      tabSelected: true,
+    },
+  },
+  {
+    name: "about:downloads, open in background tab",
+    whichUI: "aboutDownloads",
+    itemSelector: "#downloadsListBox richlistitem .downloadContainer",
+    async userEvents(itemSelector, win) {
+      let browser = win.gBrowser.selectedBrowser;
+      is(browser.currentURI.spec, "about:downloads");
+      await contentTriggerDblclickOn(
+        itemSelector,
+        { ctrlKey: true, metaKey: true, shiftKey: true },
+        browser
+      );
+    },
+    expected: {
+      downloadCount: 1,
+      newWindow: false,
+      opensTab: true,
+      tabSelected: false,
+    },
+  },
+  {
+    name: "Private download in about:downloads, opens in new private window",
+    skip: true, // Bug 1641770
+    whichUI: "aboutDownloads",
+    itemSelector: "#downloadsListBox richlistitem .downloadContainer",
+    async userEvents(itemSelector, win) {
+      let browser = win.gBrowser.selectedBrowser;
+      is(browser.currentURI.spec, "about:downloads");
+      await contentTriggerDblclickOn(itemSelector, { shiftKey: true }, browser);
+    },
+    isPrivate: true,
+    expected: {
+      downloadCount: 1,
+      newWindow: true,
+      opensTab: false,
+      tabSelected: true,
+    },
+  },
+];
+
+function triggerDblclickOn(target, modifiers = {}, win) {
+  let promise = BrowserTestUtils.waitForEvent(target, "dblclick");
+  EventUtils.synthesizeMouseAtCenter(
+    target,
+    Object.assign({ clickCount: 1 }, modifiers),
+    win
+  );
+  EventUtils.synthesizeMouseAtCenter(
+    target,
+    Object.assign({ clickCount: 2 }, modifiers),
+    win
+  );
+  return promise;
+}
+
+function contentTriggerDblclickOn(selector, eventModifiers = {}, browser) {
+  return SpecialPowers.spawn(
+    browser,
+    [selector, eventModifiers],
+    async function(itemSelector, modifiers) {
+      const EventUtils = ContentTaskUtils.getEventUtils(content);
+      let itemTarget = content.document.querySelector(itemSelector);
+      ok(itemTarget, "Download item target exists");
+
+      let doubleClicked = ContentTaskUtils.waitForEvent(itemTarget, "dblclick");
+      // NOTE: we are using sendMouseEvent instead of synthesizeMouseAtCenter
+      // here to prevent an unexpected timeout failure in devedition builds
+      // due to the ContentTaskUtils.waitForEvent promise never been resolved.
+      EventUtils.sendMouseEvent(
+        { type: "dblclick", ...modifiers },
+        itemTarget,
+        content
+      );
+      info("Waiting for double-click content task");
+      await doubleClicked;
+    }
+  );
+}
+
+async function verifyContextMenu(contextMenu, expected = {}) {
+  info("verifyContextMenu with expected: " + JSON.stringify(expected, null, 2));
+  let alwaysMenuItem = contextMenu.querySelector(
+    ".downloadAlwaysUseSystemDefaultMenuItem"
+  );
+  let useSystemMenuItem = contextMenu.querySelector(
+    ".downloadUseSystemDefaultMenuItem"
+  );
+  info("Waiting for the context menu to show up");
+  await TestUtils.waitForCondition(
+    () => BrowserTestUtils.is_visible(contextMenu),
+    "The context menu is visible"
+  );
+  await TestUtils.waitForTick();
+
+  info("Checking visibility of the system viewer menu items");
+  is(
+    BrowserTestUtils.is_hidden(useSystemMenuItem),
+    expected.useSystemMenuItemDisabled,
+    `The 'Use system viewer' menu item was ${
+      expected.useSystemMenuItemDisabled ? "hidden" : "visible"
+    }`
+  );
+  is(
+    BrowserTestUtils.is_hidden(alwaysMenuItem),
+    expected.alwaysMenuItemDisabled,
+    `The 'Use system viewer' menu item was ${
+      expected.alwaysMenuItemDisabled ? "hidden" : "visible"
+    }`
+  );
+
+  if (!expected.useSystemMenuItemDisabled && expected.alwaysChecked) {
+    is(
+      alwaysMenuItem.getAttribute("checked"),
+      "true",
+      "The 'Always...' menu item is checked"
+    );
+  } else if (!expected.useSystemMenuItemDisabled) {
+    ok(
+      !alwaysMenuItem.hasAttribute("checked"),
+      "The 'Always...' menu item not checked"
+    );
+  }
+}
+
+async function addPDFDownload(itemData) {
+  let startTimeMs = Date.now();
+  info("addPDFDownload with itemData: " + JSON.stringify(itemData, null, 2));
+
+  let downloadPathname = PathUtils.join(gDownloadDir, itemData.targetFilename);
+  delete itemData.targetFilename;
+
+  info("Creating saved download file at:" + downloadPathname);
+  let pdfFile = await createDownloadedFile(downloadPathname, DATA_PDF);
+  info("Created file at:" + pdfFile.path);
+
+  let downloadList = await Downloads.getList(
+    itemData.isPrivate ? Downloads.PRIVATE : Downloads.PUBLIC
+  );
+  let download = {
+    source: {
+      url: "https://example.com/some.pdf",
+      isPrivate: itemData.isPrivate,
+    },
+    target: {
+      path: pdfFile.path,
+    },
+    succeeded: DownloadsCommon.DOWNLOAD_FINISHED,
+    canceled: false,
+    error: null,
+    hasPartialData: false,
+    hasBlockedData: itemData.hasBlockedData || false,
+    startTime: new Date(startTimeMs++),
+    ...itemData,
+  };
+  if (itemData.errorObj) {
+    download.errorObj = itemData.errorObj;
+  }
+
+  await downloadList.add(await Downloads.createDownload(download));
+  return download;
+}
+
+async function testSetup() {
+  // remove download files, empty out collections
+  let downloadList = await Downloads.getList(Downloads.ALL);
+  let downloadCount = (await downloadList.getAll()).length;
+  is(downloadCount, 0, "At the start of the test, there should be 0 downloads");
+
+  await task_resetState();
+  if (!gDownloadDir) {
+    gDownloadDir = await setDownloadDir();
+  }
+  info("Created download directory: " + gDownloadDir);
+}
+
+async function openDownloadPanel(expectedItemCount) {
+  // Open the user interface and wait for data to be fully loaded.
+  let richlistbox = document.getElementById("downloadsListBox");
+  await task_openPanel();
+  await TestUtils.waitForCondition(
+    () =>
+      richlistbox.childElementCount == expectedItemCount &&
+      !richlistbox.getAttribute("disabled")
+  );
+}
+
+async function testOpenPDFPreview({
+  name,
+  whichUI,
+  downloadProperties,
+  itemSelector,
+  expected,
+  prefs = [],
+  userEvents,
+  isPrivate,
+}) {
+  info("Test case: " + name);
+  // Wait for focus first
+  await promiseFocus();
+  await testSetup();
+  if (prefs.length) {
+    await SpecialPowers.pushPrefEnv({
+      set: prefs,
+    });
+  }
+
+  // Populate downloads database with the data required by this test.
+  info("Adding download objects");
+  if (!downloadProperties) {
+    downloadProperties = {
+      targetFilename: "downloaded.pdf",
+    };
+  }
+  let download = await addPDFDownload({
+    ...downloadProperties,
+    isPrivate,
+  });
+  info("Got download pathname:" + download.target.path);
+  is(
+    !!download.source.isPrivate,
+    !!isPrivate,
+    `Added download is ${isPrivate ? "private" : "not private"} as expected`
+  );
+  let downloadList = await Downloads.getList(
+    isPrivate ? Downloads.PRIVATE : Downloads.PUBLIC
+  );
+  let downloads = await downloadList.getAll();
+  is(
+    downloads.length,
+    expected.downloadCount,
+    `${isPrivate ? "Private" : "Public"} list has expected ${
+      downloads.length
+    } downloads`
+  );
+
+  let pdfFileURI = NetUtil.newURI(new FileUtils.File(download.target.path));
+  info("pdfFileURI:" + pdfFileURI.spec);
+
+  let uiWindow = window;
+  let previewWindow = window;
+  // we never want to unload the test browser by loading the file: URI into it
+  await BrowserTestUtils.withNewTab("about:blank", async initialBrowser => {
+    let previewTab;
+    let previewHappened;
+
+    if (expected.newWindow) {
+      info(
+        "previewHappened will wait for new browser window with url: " +
+          pdfFileURI.spec
+      );
+      // wait for a new browser window
+      previewHappened = BrowserTestUtils.waitForNewWindow({
+        anyWindow: true,
+        url: pdfFileURI.spec,
+      });
+    } else if (expected.opensTab) {
+      // wait for a tab to be opened
+      info("previewHappened will wait for tab with URI:" + pdfFileURI.spec);
+      previewHappened = BrowserTestUtils.waitForNewTab(
+        gBrowser,
+        pdfFileURI.spec,
+        false, // dont wait for load
+        true // any tab, not just the next one
+      );
+    } else {
+      info(
+        "previewHappened will wait to load " +
+          pdfFileURI.spec +
+          " into the current tab"
+      );
+      previewHappened = BrowserTestUtils.browserLoaded(
+        initialBrowser,
+        false,
+        pdfFileURI.spec
+      );
+    }
+
+    let itemTarget;
+    let contextMenu;
+
+    switch (whichUI) {
+      case "downloadPanel":
+        info("Opening download panel");
+        await openDownloadPanel(expected.downloadCount);
+        info("/Opening download panel");
+        itemTarget = document.querySelector(itemSelector);
+        contextMenu = uiWindow.document.querySelector("#downloadsContextMenu");
+
+        break;
+      case "allDownloads":
+        // we'll be interacting with the library dialog
+        uiWindow = await openLibrary("Downloads");
+
+        let listbox = uiWindow.document.getElementById("downloadsListBox");
+        ok(listbox, "download list box present");
+        // wait for the expected number of items in the view,
+        // and for the first item to be visible && clickable
+        await TestUtils.waitForCondition(() => {
+          return (
+            listbox.itemChildren.length == expected.downloadCount &&
+            BrowserTestUtils.is_visible(listbox.itemChildren[0])
+          );
+        });
+        itemTarget = listbox.itemChildren[0];
+        contextMenu = uiWindow.document.querySelector("#downloadsContextMenu");
+
+        break;
+      case "aboutDownloads":
+        info("Preparing about:downloads browser window");
+
+        // Because of bug 1329912, we sometimes get a bogus last-pb-context-exited notification
+        // which removes all the private downloads and about:downloads renders a empty list
+        // we'll allow time for that to happen before loading about:downloads
+        let pbExitedOrTimeout = isPrivate
+          ? new Promise(resolve => {
+              const topic = "last-pb-context-exited";
+              const ENOUGH_TIME = 1000;
+              function observer() {
+                info(`Bogus ${topic} observed`);
+                done();
+              }
+              function done() {
+                clearTimeout(timerId);
+                Services.obs.removeObserver(observer, topic);
+                resolve();
+              }
+              /* eslint-disable mozilla/no-arbitrary-setTimeout */
+              const timerId = setTimeout(done, ENOUGH_TIME);
+              Services.obs.addObserver(observer, "last-pb-context-exited");
+            })
+          : Promise.resolve();
+
+        if (isPrivate) {
+          uiWindow = await BrowserTestUtils.openNewBrowserWindow({
+            private: true,
+          });
+        }
+        info(
+          "in aboutDownloads, initially there are tabs: " +
+            uiWindow.gBrowser.tabs.length
+        );
+
+        let browser = uiWindow.gBrowser.selectedBrowser;
+        await pbExitedOrTimeout;
+
+        info("Loading about:downloads");
+        let downloadsLoaded = BrowserTestUtils.waitForEvent(
+          browser,
+          "InitialDownloadsLoaded",
+          true
+        );
+        BrowserTestUtils.loadURI(browser, "about:downloads");
+        await BrowserTestUtils.browserLoaded(browser);
+        info("waiting for downloadsLoaded");
+        await downloadsLoaded;
+
+        await ContentTask.spawn(
+          browser,
+          [expected.downloadCount],
+          async function awaitListItems(expectedCount) {
+            await ContentTaskUtils.waitForCondition(
+              () =>
+                content.document.getElementById("downloadsListBox")
+                  .childElementCount == expectedCount,
+              `Await ${expectedCount} download list items`
+            );
+          }
+        );
+        break;
+    }
+
+    if (contextMenu) {
+      info("trigger the contextmenu");
+      await openContextMenu(itemTarget || itemSelector, uiWindow);
+      info("context menu should be open, verify its menu items");
+      let expectedValues = {
+        useSystemMenuItemDisabled: false,
+        alwaysMenuItemDisabled: false,
+        ...expected,
+      };
+      await verifyContextMenu(contextMenu, expectedValues);
+      contextMenu.hidePopup();
+    } else {
+      todo(contextMenu, "No context menu checks for test: " + name);
+    }
+
+    info("Executing user events");
+    await userEvents(itemTarget || itemSelector, uiWindow);
+
+    info("Waiting for previewHappened");
+    let results = await previewHappened;
+    if (expected.newWindow) {
+      previewWindow = results;
+      info("New window expected, got previewWindow? " + previewWindow);
+    }
+    previewTab =
+      previewWindow.gBrowser.tabs[previewWindow.gBrowser.tabs.length - 1];
+    ok(previewTab, "Got preview tab");
+
+    let isSelected = previewWindow.gBrowser.selectedTab == previewTab;
+    if (expected.tabSelected) {
+      ok(isSelected, "The preview tab was selected");
+    } else {
+      ok(!isSelected, "The preview tab was opened in the background");
+    }
+
+    is(
+      previewTab.linkedBrowser.currentURI.spec,
+      pdfFileURI.spec,
+      "previewTab has the expected currentURI"
+    );
+
+    is(
+      PrivateBrowsingUtils.isBrowserPrivate(previewTab.linkedBrowser),
+      !!isPrivate,
+      `The preview tab was ${isPrivate ? "private" : "not private"} as expected`
+    );
+
+    info("cleaning up");
+    if (whichUI == "downloadPanel") {
+      DownloadsPanel.hidePanel();
+    }
+    let lastPBContextExitedPromise = isPrivate
+      ? TestUtils.topicObserved("last-pb-context-exited").then(() =>
+          TestUtils.waitForTick()
+        )
+      : Promise.resolve();
+
+    info("Test opened a new UI window? " + (uiWindow !== window));
+    if (uiWindow !== window) {
+      info("Closing uiWindow");
+      await BrowserTestUtils.closeWindow(uiWindow);
+    }
+    if (expected.newWindow) {
+      // will also close the previewTab
+      await BrowserTestUtils.closeWindow(previewWindow);
+    } else {
+      await BrowserTestUtils.removeTab(previewTab);
+    }
+    info("Waiting for lastPBContextExitedPromise");
+    await lastPBContextExitedPromise;
+  });
+  await downloadList.removeFinished();
+  if (prefs.length) {
+    await SpecialPowers.popPrefEnv();
+  }
+}
+
+// register the tests
+for (let testData of TestCases) {
+  if (testData.skip) {
+    info("Skipping test:" + testData.name);
+    continue;
+  }
+  // use the 'name' property of each test case as the test function name
+  // so we get useful logs
+  let tmp = {
+    async [testData.name]() {
+      await testOpenPDFPreview(testData);
+    },
+  };
+  add_task(tmp[testData.name]);
+}
diff --git a/browser/components/downloads/test/browser/browser_tempfilename.js b/browser/components/downloads/test/browser/browser_tempfilename.js
new file mode 100644
index 0000000000..dcef4016a6
--- /dev/null
+++ b/browser/components/downloads/test/browser/browser_tempfilename.js
@@ -0,0 +1,91 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+add_task(async function test_tempfilename() {
+  startServer();
+  let downloadURL = httpUrl("interruptible.txt");
+  let list = await Downloads.getList(Downloads.PUBLIC);
+  let downloadStarted = new Promise(resolve => {
+    let view = {
+      onDownloadAdded(download) {
+        list.removeView(view);
+        resolve(download);
+      },
+    };
+    list.addView(view);
+  });
+
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["browser.download.improvements_to_download_panel", true],
+      ["browser.download.always_ask_before_handling_new_types", false],
+    ],
+  });
+
+  const MimeSvc = Cc["@mozilla.org/mime;1"].getService(Ci.nsIMIMEService);
+  const HandlerSvc = Cc["@mozilla.org/uriloader/handler-service;1"].getService(
+    Ci.nsIHandlerService
+  );
+  let mimeInfo = MimeSvc.getFromTypeAndExtension(
+    HandlerSvc.getTypeFromExtension("txt"),
+    "txt"
+  );
+  let existed = HandlerSvc.exists(mimeInfo);
+  mimeInfo.alwaysAskBeforeHandling = false;
+  mimeInfo.preferredAction = Ci.nsIHandlerInfo.saveToDisk;
+  HandlerSvc.store(mimeInfo);
+
+  serveInterruptibleAsDownload();
+  mustInterruptResponses();
+  await BrowserTestUtils.withNewTab(
+    {
+      gBrowser,
+      url: downloadURL,
+      waitForLoad: false,
+      waitForStop: true,
+    },
+    async () => {
+      let download = await downloadStarted;
+      registerCleanupFunction(async () => {
+        if (existed) {
+          HandlerSvc.store(mimeInfo);
+        } else {
+          HandlerSvc.remove(mimeInfo);
+        }
+        await download.finalize(true);
+        if (Services.appinfo.OS === "WINNT") {
+          // We need to make the file writable to delete it on Windows.
+          await IOUtils.setPermissions(download.target.path, 0o600);
+        }
+        await IOUtils.remove(download.target.path);
+        await download.finalize();
+        await list.removeFinished();
+      });
+
+      let { partFilePath } = download.target;
+      Assert.stringContains(
+        partFilePath,
+        "interruptible",
+        "Should keep bit of original filename."
+      );
+      isnot(
+        PathUtils.filename(partFilePath),
+        "interruptible.txt.part",
+        "Should not just have original filename."
+      );
+      ok(
+        partFilePath.endsWith(".txt.part"),
+        `${PathUtils.filename(partFilePath)} should end with .txt.part`
+      );
+      let promiseFinished = download.whenSucceeded();
+      continueResponses();
+      await promiseFinished;
+      ok(
+        !(await IOUtils.exists(download.target.partFilePath)),
+        "Temp file should be gone."
+      );
+    }
+  );
+});
diff --git a/browser/components/downloads/test/browser/foo.txt b/browser/components/downloads/test/browser/foo.txt
new file mode 100644
index 0000000000..77e7195596
--- /dev/null
+++ b/browser/components/downloads/test/browser/foo.txt
@@ -0,0 +1 @@
+Dummy content for unknownContentType_dialog_layout_data.txt
diff --git a/browser/components/downloads/test/browser/foo.txt^headers^ b/browser/components/downloads/test/browser/foo.txt^headers^
new file mode 100644
index 0000000000..2a3c472e26
--- /dev/null
+++ b/browser/components/downloads/test/browser/foo.txt^headers^
@@ -0,0 +1,2 @@
+Content-Type: text/plain
+Content-Disposition: attachment
diff --git a/browser/components/downloads/test/browser/head.js b/browser/components/downloads/test/browser/head.js
new file mode 100644
index 0000000000..1fdbe743b9
--- /dev/null
+++ b/browser/components/downloads/test/browser/head.js
@@ -0,0 +1,448 @@
+/* -*- indent-tabs-mode: nil; js-indent-level: 2 -*- */
+/* vim: set ts=2 et sw=2 tw=80: */
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+/**
+ * Provides infrastructure for automated download components tests.
+ */
+
+// Globals
+
+ChromeUtils.defineESModuleGetters(this, {
+  Downloads: "resource://gre/modules/Downloads.sys.mjs",
+  DownloadsCommon: "resource:///modules/DownloadsCommon.sys.mjs",
+  FileUtils: "resource://gre/modules/FileUtils.sys.mjs",
+  PlacesUtils: "resource://gre/modules/PlacesUtils.sys.mjs",
+});
+ChromeUtils.defineModuleGetter(
+  this,
+  "HttpServer",
+  "resource://testing-common/httpd.js"
+);
+
+let gTestTargetFile = new FileUtils.File(
+  PathUtils.join(
+    Services.dirsvc.get("TmpD", Ci.nsIFile).path,
+    "dm-ui-test.file"
+  )
+);
+
+gTestTargetFile.createUnique(Ci.nsIFile.NORMAL_FILE_TYPE, FileUtils.PERMS_FILE);
+Services.prefs.setIntPref("security.dialog_enable_delay", 0);
+
+// The file may have been already deleted when removing a paused download.
+// Also clear security.dialog_enable_delay pref.
+registerCleanupFunction(async () => {
+  Services.prefs.clearUserPref("security.dialog_enable_delay");
+
+  if (await IOUtils.exists(gTestTargetFile.path)) {
+    info("removing " + gTestTargetFile.path);
+    if (Services.appinfo.OS === "WINNT") {
+      // We need to make the file writable to delete it on Windows.
+      await IOUtils.setPermissions(gTestTargetFile.path, 0o600);
+    }
+    await IOUtils.remove(gTestTargetFile.path);
+  }
+});
+
+const DATA_PDF = atob(
+  "JVBERi0xLjANCjEgMCBvYmo8PC9UeXBlL0NhdGFsb2cvUGFnZXMgMiAwIFI+PmVuZG9iaiAyIDAgb2JqPDwvVHlwZS9QYWdlcy9LaWRzWzMgMCBSXS9Db3VudCAxPj5lbmRvYmogMyAwIG9iajw8L1R5cGUvUGFnZS9NZWRpYUJveFswIDAgMyAzXT4+ZW5kb2JqDQp4cmVmDQowIDQNCjAwMDAwMDAwMDAgNjU1MzUgZg0KMDAwMDAwMDAxMCAwMDAwMCBuDQowMDAwMDAwMDUzIDAwMDAwIG4NCjAwMDAwMDAxMDIgMDAwMDAgbg0KdHJhaWxlcjw8L1NpemUgNC9Sb290IDEgMCBSPj4NCnN0YXJ0eHJlZg0KMTQ5DQolRU9G"
+);
+
+const TEST_DATA_SHORT = "This test string is downloaded.";
+
+/**
+ * This is an internal reference that should not be used directly by tests.
+ */
+var _gDeferResponses = PromiseUtils.defer();
+
+/**
+ * Ensures that all the interruptible requests started after this function is
+ * called won't complete until the continueResponses function is called.
+ *
+ * Normally, the internal HTTP server returns all the available data as soon as
+ * a request is received.  In order for some requests to be served one part at a
+ * time, special interruptible handlers are registered on the HTTP server.  This
+ * allows testing events or actions that need to happen in the middle of a
+ * download.
+ *
+ * For example, the handler accessible at the httpUri("interruptible.txt")
+ * address returns the TEST_DATA_SHORT text, then it may block until the
+ * continueResponses method is called.  At this point, the handler sends the
+ * TEST_DATA_SHORT text again to complete the response.
+ *
+ * If an interruptible request is started before the function is called, it may
+ * or may not be blocked depending on the actual sequence of events.
+ */
+function mustInterruptResponses() {
+  // If there are pending blocked requests, allow them to complete.  This is
+  // done to prevent requests from being blocked forever, but should not affect
+  // the test logic, since previously started requests should not be monitored
+  // on the client side anymore.
+  _gDeferResponses.resolve();
+
+  info("Interruptible responses will be blocked midway.");
+  _gDeferResponses = PromiseUtils.defer();
+}
+
+/**
+ * Allows all the current and future interruptible requests to complete.
+ */
+function continueResponses() {
+  info("Interruptible responses are now allowed to continue.");
+  _gDeferResponses.resolve();
+}
+
+/**
+ * Creates a download, which could be interrupted in the middle of it's progress.
+ */
+function promiseInterruptibleDownload(extension = ".txt") {
+  let interruptibleFile = FileUtils.getFile("TmpD", [
+    `interruptible${extension}`,
+  ]);
+  interruptibleFile.createUnique(
+    Ci.nsIFile.NORMAL_FILE_TYPE,
+    FileUtils.PERMS_FILE
+  );
+
+  registerCleanupFunction(async () => {
+    if (await IOUtils.exists(interruptibleFile.path)) {
+      if (Services.appinfo.OS === "WINNT") {
+        // We need to make the file writable to delete it on Windows.
+        await IOUtils.setPermissions(interruptibleFile.path, 0o600);
+      }
+      await IOUtils.remove(interruptibleFile.path);
+    }
+  });
+
+  return Downloads.createDownload({
+    source: httpUrl("interruptible.txt"),
+    target: { path: interruptibleFile.path },
+  });
+}
+
+// Asynchronous support subroutines
+
+async function createDownloadedFile(pathname, contents) {
+  let file = new FileUtils.File(pathname);
+  if (file.exists()) {
+    info(`File at ${pathname} already exists`);
+  }
+  // No post-test cleanup necessary; tmp downloads directory is already removed after each test
+  await IOUtils.writeUTF8(pathname, contents);
+  ok(file.exists(), `Created ${pathname}`);
+  return file;
+}
+
+async function openContextMenu(itemElement, win = window) {
+  let popupShownPromise = BrowserTestUtils.waitForEvent(
+    itemElement.ownerDocument,
+    "popupshown"
+  );
+  EventUtils.synthesizeMouseAtCenter(
+    itemElement,
+    {
+      type: "contextmenu",
+      button: 2,
+    },
+    win
+  );
+  let { target } = await popupShownPromise;
+  return target;
+}
+
+function promiseFocus() {
+  return new Promise(resolve => {
+    waitForFocus(resolve);
+  });
+}
+
+function promisePanelOpened() {
+  if (DownloadsPanel.panel && DownloadsPanel.panel.state == "open") {
+    return Promise.resolve();
+  }
+
+  return new Promise(resolve => {
+    // Hook to wait until the panel is shown.
+    let originalOnPopupShown = DownloadsPanel.onPopupShown;
+    DownloadsPanel.onPopupShown = function() {
+      DownloadsPanel.onPopupShown = originalOnPopupShown;
+      originalOnPopupShown.apply(this, arguments);
+
+      // Defer to the next tick of the event loop so that we don't continue
+      // processing during the DOM event handler itself.
+      setTimeout(resolve, 0);
+    };
+  });
+}
+
+async function task_resetState() {
+  // Remove all downloads.
+  let publicList = await Downloads.getList(Downloads.PUBLIC);
+  let downloads = await publicList.getAll();
+  for (let download of downloads) {
+    await publicList.remove(download);
+    if (await IOUtils.exists(download.target.path)) {
+      await download.finalize(true);
+      info("removing " + download.target.path);
+      if (Services.appinfo.OS === "WINNT") {
+        // We need to make the file writable to delete it on Windows.
+        await IOUtils.setPermissions(download.target.path, 0o600);
+      }
+      await IOUtils.remove(download.target.path);
+    }
+  }
+
+  DownloadsPanel.hidePanel();
+
+  await promiseFocus();
+}
+
+async function task_addDownloads(aItems) {
+  let startTimeMs = Date.now();
+
+  let publicList = await Downloads.getList(Downloads.PUBLIC);
+  for (let item of aItems) {
+    let source = {
+      url: "http://www.example.com/test-download.txt",
+      ...item.source,
+    };
+    let target =
+      item.target instanceof Ci.nsIFile
+        ? item.target
+        : {
+            path: gTestTargetFile.path,
+            ...item.target,
+          };
+
+    let download = {
+      source,
+      target,
+      succeeded: item.state == DownloadsCommon.DOWNLOAD_FINISHED,
+      canceled:
+        item.state == DownloadsCommon.DOWNLOAD_CANCELED ||
+        item.state == DownloadsCommon.DOWNLOAD_PAUSED,
+      deleted: item.deleted ?? false,
+      error:
+        item.state == DownloadsCommon.DOWNLOAD_FAILED
+          ? new Error("Failed.")
+          : null,
+      hasPartialData: item.state == DownloadsCommon.DOWNLOAD_PAUSED,
+      hasBlockedData: item.hasBlockedData || false,
+      openDownloadsListOnStart: item.openDownloadsListOnStart ?? true,
+      contentType: item.contentType,
+      startTime: new Date(startTimeMs++),
+    };
+    // `"errorObj" in download` must be false when there's no error.
+    if (item.errorObj) {
+      download.errorObj = item.errorObj;
+    }
+    download = await Downloads.createDownload(download);
+    await publicList.add(download);
+    await download.refresh();
+  }
+}
+
+async function task_openPanel() {
+  await promiseFocus();
+
+  let promise = promisePanelOpened();
+  DownloadsPanel.showPanel();
+  await promise;
+}
+
+async function setDownloadDir() {
+  let tmpDir = PathUtils.join(
+    PathUtils.tempDir,
+    "testsavedir" + Math.floor(Math.random() * 2 ** 32)
+  );
+  // Create this dir if it doesn't exist (ignores existing dirs)
+  await IOUtils.makeDirectory(tmpDir);
+  registerCleanupFunction(async function() {
+    try {
+      await IOUtils.remove(tmpDir, { recursive: true });
+    } catch (e) {
+      console.error(e);
+    }
+  });
+  Services.prefs.setIntPref("browser.download.folderList", 2);
+  Services.prefs.setCharPref("browser.download.dir", tmpDir);
+  return tmpDir;
+}
+
+let gHttpServer = null;
+let gShouldServeInterruptibleFileAsDownload = false;
+function startServer() {
+  gHttpServer = new HttpServer();
+  gHttpServer.start(-1);
+  registerCleanupFunction(() => {
+    return new Promise(resolve => {
+      // Ensure all the pending HTTP requests have a chance to finish.
+      continueResponses();
+      // Stop the HTTP server, calling resolve when it's done.
+      gHttpServer.stop(resolve);
+    });
+  });
+
+  gHttpServer.identity.setPrimary(
+    "http",
+    "www.example.com",
+    gHttpServer.identity.primaryPort
+  );
+
+  gHttpServer.registerPathHandler("/file1.txt", (request, response) => {
+    response.setStatusLine(null, 200, "OK");
+    response.write("file1");
+    response.processAsync();
+    response.finish();
+  });
+  gHttpServer.registerPathHandler("/file2.txt", (request, response) => {
+    response.setStatusLine(null, 200, "OK");
+    response.write("file2");
+    response.processAsync();
+    response.finish();
+  });
+  gHttpServer.registerPathHandler("/file3.txt", (request, response) => {
+    response.setStatusLine(null, 200, "OK");
+    response.write("file3");
+    response.processAsync();
+    response.finish();
+  });
+
+  gHttpServer.registerPathHandler("/interruptible.txt", function(
+    aRequest,
+    aResponse
+  ) {
+    info("Interruptible request started.");
+
+    // Process the first part of the response.
+    aResponse.processAsync();
+    aResponse.setHeader("Content-Type", "text/plain", false);
+    if (gShouldServeInterruptibleFileAsDownload) {
+      aResponse.setHeader("Content-Disposition", "attachment");
+    }
+    aResponse.setHeader(
+      "Content-Length",
+      "" + TEST_DATA_SHORT.length * 2,
+      false
+    );
+    aResponse.write(TEST_DATA_SHORT);
+
+    // Wait on the current deferred object, then finish the request.
+    _gDeferResponses.promise
+      .then(function RIH_onSuccess() {
+        aResponse.write(TEST_DATA_SHORT);
+        aResponse.finish();
+        info("Interruptible request finished.");
+      })
+      .catch(Cu.reportError);
+  });
+}
+
+function serveInterruptibleAsDownload() {
+  gShouldServeInterruptibleFileAsDownload = true;
+  registerCleanupFunction(
+    () => (gShouldServeInterruptibleFileAsDownload = false)
+  );
+}
+
+function httpUrl(aFileName) {
+  return (
+    "http://localhost:" + gHttpServer.identity.primaryPort + "/" + aFileName
+  );
+}
+
+function openLibrary(aLeftPaneRoot) {
+  let library = window.openDialog(
+    "chrome://browser/content/places/places.xhtml",
+    "",
+    "chrome,toolbar=yes,dialog=no,resizable",
+    aLeftPaneRoot
+  );
+
+  return new Promise(resolve => {
+    waitForFocus(resolve, library);
+  });
+}
+
+/**
+ * Waits for a download to reach its progress, in case it has not
+ * reached the expected progress already.
+ *
+ * @param aDownload
+ *        The Download object to wait upon.
+ *
+ * @return {Promise}
+ * @resolves When the download has reached its progress.
+ * @rejects Never.
+ */
+function promiseDownloadHasProgress(aDownload, progress) {
+  return new Promise(resolve => {
+    // Wait for the download to reach its progress.
+    let onchange = function() {
+      let downloadInProgress =
+        !aDownload.stopped && aDownload.progress == progress;
+      let downloadFinished =
+        progress == 100 &&
+        aDownload.progress == progress &&
+        aDownload.succeeded;
+      if (downloadInProgress || downloadFinished) {
+        info(`Download reached ${progress}%`);
+        aDownload.onchange = null;
+        resolve();
+      }
+    };
+
+    // Register for the notification, but also call the function directly in
+    // case the download already reached the expected progress.
+    aDownload.onchange = onchange;
+    onchange();
+  });
+}
+
+/**
+ * Waits for a given button to become visible.
+ */
+function promiseButtonShown(id) {
+  let dwu = window.windowUtils;
+  return BrowserTestUtils.waitForCondition(() => {
+    let target = document.getElementById(id);
+    let bounds = dwu.getBoundsWithoutFlushing(target);
+    return bounds.width > 0 && bounds.height > 0;
+  }, `Waiting for button ${id} to have non-0 size`);
+}
+
+async function simulateDropAndCheck(win, dropTarget, urls) {
+  let dragData = [[{ type: "text/plain", data: urls.join("\n") }]];
+  let list = await Downloads.getList(Downloads.ALL);
+
+  let added = new Set();
+  let succeeded = new Set();
+  await new Promise(resolve => {
+    let view = {
+      onDownloadAdded(download) {
+        added.add(download.source.url);
+      },
+      onDownloadChanged(download) {
+        if (!added.has(download.source.url)) {
+          return;
+        }
+        if (!download.succeeded) {
+          return;
+        }
+        succeeded.add(download.source.url);
+        if (succeeded.size == urls.length) {
+          list.removeView(view).then(resolve);
+        }
+      },
+    };
+    list.addView(view).then(function() {
+      EventUtils.synthesizeDrop(dropTarget, dropTarget, dragData, "link", win);
+    });
+  });
+
+  for (let url of urls) {
+    ok(added.has(url), url + " is added to download");
+  }
+}
diff --git a/browser/components/downloads/test/browser/not-really-a-jpeg.jpeg b/browser/components/downloads/test/browser/not-really-a-jpeg.jpeg
new file mode 100644
index 0000000000..04b7f003b4
--- /dev/null
+++ b/browser/components/downloads/test/browser/not-really-a-jpeg.jpeg
diff --git a/browser/components/downloads/test/browser/not-really-a-jpeg.jpeg^headers^ b/browser/components/downloads/test/browser/not-really-a-jpeg.jpeg^headers^
new file mode 100644
index 0000000000..c1a7794310
--- /dev/null
+++ b/browser/components/downloads/test/browser/not-really-a-jpeg.jpeg^headers^
@@ -0,0 +1,2 @@
+Content-Type: image/webp
+
diff --git a/browser/components/downloads/test/browser/test_spammy_page.html b/browser/components/downloads/test/browser/test_spammy_page.html
new file mode 100644
index 0000000000..92332bb1c0
--- /dev/null
+++ b/browser/components/downloads/test/browser/test_spammy_page.html
@@ -0,0 +1,26 @@
+<!-- Any copyright is dedicated to the Public Domain.
+   - http://creativecommons.org/publicdomain/zero/1.0/ -->
+<!DOCTYPE html>
+<html>
+<head>
+	<meta charset="utf-8" />
+	<title>Spam Page Test</title>
+</head>
+<body>
+	<p> Hello, it's the spammy page! </p>
+<script type="text/javascript">
+	let count = 0;
+window.onload = window.onclick = function() {
+  if (count < 100) {
+	count++;
+	let l = document.createElement('a');
+	l.href = 'data:text/plain,some text';
+	l.download = 'sometext.txt';
+
+	document.body.appendChild(l);
+	l.click();
+  }
+}
+</script>
+</body>
+</html>
diff --git a/browser/components/downloads/test/unit/head.js b/browser/components/downloads/test/unit/head.js
new file mode 100644
index 0000000000..26420497f9
--- /dev/null
+++ b/browser/components/downloads/test/unit/head.js
@@ -0,0 +1,67 @@
+ChromeUtils.defineESModuleGetters(this, {
+  Downloads: "resource://gre/modules/Downloads.sys.mjs",
+  DownloadsCommon: "resource:///modules/DownloadsCommon.sys.mjs",
+  FileTestUtils: "resource://testing-common/FileTestUtils.sys.mjs",
+  FileUtils: "resource://gre/modules/FileUtils.sys.mjs",
+  TestUtils: "resource://testing-common/TestUtils.sys.mjs",
+});
+ChromeUtils.defineModuleGetter(
+  this,
+  "NetUtil",
+  "resource://gre/modules/NetUtil.jsm"
+);
+
+async function createDownloadedFile(pathname, contents) {
+  info("createDownloadedFile: " + pathname);
+  let file = new FileUtils.File(pathname);
+  if (file.exists()) {
+    info(`File at ${pathname} already exists`);
+    if (!contents) {
+      ok(
+        false,
+        `A file already exists at ${pathname}, but createDownloadedFile was asked to create a non-existant file`
+      );
+    }
+  }
+  if (contents) {
+    await IOUtils.writeUTF8(pathname, contents);
+    ok(file.exists(), `Created ${pathname}`);
+  }
+  // No post-test cleanup necessary; tmp downloads directory is already removed after each test
+  return file;
+}
+
+let gDownloadDir;
+
+async function setDownloadDir() {
+  let tmpDir = Services.dirsvc.get("TmpD", Ci.nsIFile).path;
+  tmpDir = PathUtils.join(
+    tmpDir,
+    "testsavedir" + Math.floor(Math.random() * 2 ** 32)
+  );
+  // Create this dir if it doesn't exist (ignores existing dirs)
+  await IOUtils.makeDirectory(tmpDir);
+  registerCleanupFunction(async function() {
+    try {
+      await IOUtils.remove(tmpDir, { recursive: true });
+    } catch (e) {
+      console.error(e);
+    }
+  });
+  Services.prefs.setIntPref("browser.download.folderList", 2);
+  Services.prefs.setCharPref("browser.download.dir", tmpDir);
+  return tmpDir;
+}
+
+/**
+ * All the tests are implemented with add_task, this starts them automatically.
+ */
+function run_test() {
+  do_get_profile();
+  run_next_test();
+}
+
+add_setup(async function test_common_initialize() {
+  gDownloadDir = await setDownloadDir();
+  Services.prefs.setCharPref("browser.download.loglevel", "Debug");
+});
diff --git a/browser/components/downloads/test/unit/test_DownloadsCommon_getMimeInfo.js b/browser/components/downloads/test/unit/test_DownloadsCommon_getMimeInfo.js
new file mode 100644
index 0000000000..5c150564b1
--- /dev/null
+++ b/browser/components/downloads/test/unit/test_DownloadsCommon_getMimeInfo.js
@@ -0,0 +1,173 @@
+const DATA_PDF = atob(
+  "JVBERi0xLjANCjEgMCBvYmo8PC9UeXBlL0NhdGFsb2cvUGFnZXMgMiAwIFI+PmVuZG9iaiAyIDAgb2JqPDwvVHlwZS9QYWdlcy9LaWRzWzMgMCBSXS9Db3VudCAxPj5lbmRvYmogMyAwIG9iajw8L1R5cGUvUGFnZS9NZWRpYUJveFswIDAgMyAzXT4+ZW5kb2JqDQp4cmVmDQowIDQNCjAwMDAwMDAwMDAgNjU1MzUgZg0KMDAwMDAwMDAxMCAwMDAwMCBuDQowMDAwMDAwMDUzIDAwMDAwIG4NCjAwMDAwMDAxMDIgMDAwMDAgbg0KdHJhaWxlcjw8L1NpemUgNC9Sb290IDEgMCBSPj4NCnN0YXJ0eHJlZg0KMTQ5DQolRU9G"
+);
+
+const DOWNLOAD_TEMPLATE = {
+  source: {
+    url: "https://example.com/download",
+  },
+  target: {
+    path: "",
+  },
+  contentType: "text/plain",
+  succeeded: DownloadsCommon.DOWNLOAD_FINISHED,
+  canceled: false,
+  error: null,
+  hasPartialData: false,
+  hasBlockedData: false,
+  startTime: new Date(Date.now() - 1000),
+};
+
+const TESTFILES = {
+  "download-test.txt": "Text file contents\n",
+  "download-test.pdf": DATA_PDF,
+  "download-test.PDF": DATA_PDF,
+  "download-test.xxunknown": "Unknown file contents\n",
+  "download-test": "No extension file contents\n",
+};
+let gPublicList;
+
+add_task(async function test_setup() {
+  let profileDir = Services.dirsvc.get("ProfD", Ci.nsIFile).path;
+  Assert.ok(profileDir, "profileDir: " + profileDir);
+  for (let [filename, contents] of Object.entries(TESTFILES)) {
+    TESTFILES[filename] = await createDownloadedFile(
+      PathUtils.join(gDownloadDir, filename),
+      contents
+    );
+  }
+  gPublicList = await Downloads.getList(Downloads.PUBLIC);
+});
+
+const TESTCASES = [
+  {
+    name: "Check returned value is null when the download did not succeed",
+    testFile: "download-test.txt",
+    contentType: "text/plain",
+    succeeded: false,
+    expected: null,
+  },
+  {
+    name:
+      "Check correct mime-info is returned when download contentType is unambiguous",
+    testFile: "download-test.txt",
+    contentType: "text/plain",
+    expected: {
+      type: "text/plain",
+    },
+  },
+  {
+    name:
+      "Returns correct mime-info from file extension when download contentType is missing",
+    testFile: "download-test.pdf",
+    contentType: undefined,
+    expected: {
+      type: "application/pdf",
+    },
+  },
+  {
+    name: "Returns correct mime-info from file extension case-insensitively",
+    testFile: "download-test.PDF",
+    contentType: undefined,
+    expected: {
+      type: "application/pdf",
+    },
+  },
+  {
+    name:
+      "Returns null when contentType is missing and file extension is unknown",
+    testFile: "download-test.xxunknown",
+    contentType: undefined,
+    expected: null,
+  },
+  {
+    name:
+      "Returns contentType when contentType is ambiguous and file extension is unknown",
+    testFile: "download-test.xxunknown",
+    contentType: "application/octet-stream",
+    expected: {
+      type: "application/octet-stream",
+    },
+  },
+  {
+    name:
+      "Returns contentType when contentType is ambiguous and there is no file extension",
+    testFile: "download-test",
+    contentType: "application/octet-stream",
+    expected: {
+      type: "application/octet-stream",
+    },
+  },
+  {
+    name: "Returns null when there's no contentType and no file extension",
+    testFile: "download-test",
+    contentType: undefined,
+    expected: null,
+  },
+];
+
+// add tests for each of the generic mime-types we recognize,
+// to ensure they prefer the associated mime-type of the target file extension
+for (let type of [
+  "application/octet-stream",
+  "binary/octet-stream",
+  "application/unknown",
+]) {
+  TESTCASES.push({
+    name: `Returns correct mime-info from file extension when contentType is generic (${type})`,
+    testFile: "download-test.pdf",
+    contentType: type,
+    expected: {
+      type: "application/pdf",
+    },
+  });
+}
+
+for (let testData of TESTCASES) {
+  let tmp = {
+    async [testData.name]() {
+      info("testing with: " + JSON.stringify(testData));
+      await test_getMimeInfo_basic_function(testData);
+    },
+  };
+  add_task(tmp[testData.name]);
+}
+
+/**
+ * Sanity test the DownloadsCommon.getMimeInfo method with test parameters
+ */
+async function test_getMimeInfo_basic_function(testData) {
+  let downloadData = {
+    ...DOWNLOAD_TEMPLATE,
+    source: "source" in testData ? testData.source : DOWNLOAD_TEMPLATE.source,
+    succeeded:
+      "succeeded" in testData
+        ? testData.succeeded
+        : DOWNLOAD_TEMPLATE.succeeded,
+    target: TESTFILES[testData.testFile],
+    contentType: testData.contentType,
+  };
+  Assert.ok(downloadData.target instanceof Ci.nsIFile, "target is a nsIFile");
+  let download = await Downloads.createDownload(downloadData);
+  await gPublicList.add(download);
+  await download.refresh();
+
+  Assert.ok(
+    await IOUtils.exists(download.target.path),
+    "The file should actually exist."
+  );
+  let result = await DownloadsCommon.getMimeInfo(download);
+  if (testData.expected) {
+    Assert.equal(
+      result.type,
+      testData.expected.type,
+      "Got expected mimeInfo.type"
+    );
+  } else {
+    Assert.equal(
+      result,
+      null,
+      `Expected null, got object with type: ${result?.type}`
+    );
+  }
+}
diff --git a/browser/components/downloads/test/unit/test_DownloadsCommon_isFileOfType.js b/browser/components/downloads/test/unit/test_DownloadsCommon_isFileOfType.js
new file mode 100644
index 0000000000..dd4b6b62f7
--- /dev/null
+++ b/browser/components/downloads/test/unit/test_DownloadsCommon_isFileOfType.js
@@ -0,0 +1,150 @@
+const DATA_PDF = atob(
+  "JVBERi0xLjANCjEgMCBvYmo8PC9UeXBlL0NhdGFsb2cvUGFnZXMgMiAwIFI+PmVuZG9iaiAyIDAgb2JqPDwvVHlwZS9QYWdlcy9LaWRzWzMgMCBSXS9Db3VudCAxPj5lbmRvYmogMyAwIG9iajw8L1R5cGUvUGFnZS9NZWRpYUJveFswIDAgMyAzXT4+ZW5kb2JqDQp4cmVmDQowIDQNCjAwMDAwMDAwMDAgNjU1MzUgZg0KMDAwMDAwMDAxMCAwMDAwMCBuDQowMDAwMDAwMDUzIDAwMDAwIG4NCjAwMDAwMDAxMDIgMDAwMDAgbg0KdHJhaWxlcjw8L1NpemUgNC9Sb290IDEgMCBSPj4NCnN0YXJ0eHJlZg0KMTQ5DQolRU9G"
+);
+
+const DOWNLOAD_TEMPLATE = {
+  source: {
+    url: "https://download-test.com/download",
+  },
+  target: {
+    path: "",
+  },
+  contentType: "text/plain",
+  succeeded: DownloadsCommon.DOWNLOAD_FINISHED,
+  canceled: false,
+  error: null,
+  hasPartialData: false,
+  hasBlockedData: false,
+  startTime: new Date(Date.now() - 1000),
+};
+
+const TESTFILES = {
+  "download-test.pdf": DATA_PDF,
+  "download-test.xxunknown": DATA_PDF,
+  "download-test-missing.pdf": null,
+};
+let gPublicList;
+add_task(async function test_setup() {
+  let profileDir = Services.dirsvc.get("ProfD", Ci.nsIFile).path;
+  Assert.ok(profileDir, "profileDir: " + profileDir);
+  for (let [filename, contents] of Object.entries(TESTFILES)) {
+    TESTFILES[filename] = await createDownloadedFile(
+      PathUtils.join(gDownloadDir, filename),
+      contents
+    );
+  }
+  gPublicList = await Downloads.getList(Downloads.PUBLIC);
+});
+
+const TESTCASES = [
+  {
+    name: "Null download arg",
+    typeArg: "application/pdf",
+    downloadProps: null,
+    expected: /TypeError/,
+  },
+  {
+    name: "Missing type arg",
+    typeArg: undefined,
+    downloadProps: {
+      target: "download-test.pdf",
+    },
+    expected: /TypeError/,
+  },
+  {
+    name: "Empty string type arg",
+    typeArg: "",
+    downloadProps: {
+      target: "download-test.pdf",
+    },
+    expected: false,
+  },
+  {
+    name:
+      "download succeeded, file exists, unknown extension but contentType matches",
+    typeArg: "application/pdf",
+    downloadProps: {
+      target: "download-test.xxunknown",
+      contentType: "application/pdf",
+    },
+    expected: true,
+  },
+  {
+    name:
+      "download succeeded, file exists, contentType is generic and file extension maps to matching mime-type",
+    typeArg: "application/pdf",
+    downloadProps: {
+      target: "download-test.pdf",
+      contentType: "application/unknown",
+    },
+    expected: true,
+  },
+  {
+    name: "download did not succeed",
+    typeArg: "application/pdf",
+    downloadProps: {
+      target: "download-test.pdf",
+      contentType: "application/pdf",
+      succeeded: false,
+    },
+    expected: false,
+  },
+  {
+    name: "file does not exist",
+    typeArg: "application/pdf",
+    downloadProps: {
+      target: "download-test-missing.pdf",
+      contentType: "application/pdf",
+    },
+    expected: false,
+  },
+  {
+    name:
+      "contentType is missing and file extension doesnt map to a known mime-type",
+    typeArg: "application/pdf",
+    downloadProps: {
+      contentType: undefined,
+      target: "download-test.xxunknown",
+    },
+    expected: false,
+  },
+];
+
+for (let testData of TESTCASES) {
+  let tmp = {
+    async [testData.name]() {
+      info("testing with: " + JSON.stringify(testData));
+      await test_isFileOfType(testData);
+    },
+  };
+  add_task(tmp[testData.name]);
+}
+
+/**
+ * Sanity test the DownloadsCommon.isFileOfType method with test parameters
+ */
+async function test_isFileOfType({ name, typeArg, downloadProps, expected }) {
+  let download, result;
+  if (downloadProps) {
+    let downloadData = {
+      ...DOWNLOAD_TEMPLATE,
+      ...downloadProps,
+    };
+    downloadData.target = TESTFILES[downloadData.target];
+    Assert.ok(downloadData.target instanceof Ci.nsIFile, "target is a nsIFile");
+    download = await Downloads.createDownload(downloadData);
+    await gPublicList.add(download);
+    await download.refresh();
+  }
+
+  if (typeof expected == "boolean") {
+    result = await DownloadsCommon.isFileOfType(download, typeArg);
+    Assert.equal(result, expected, "Expected result from call to isFileOfType");
+  } else {
+    Assert.throws(
+      () => DownloadsCommon.isFileOfType(download, typeArg),
+      expected,
+      "isFileOfType should throw an exception if either the download object or mime-type arguments are falsey"
+    );
+  }
+}
diff --git a/browser/components/downloads/test/unit/test_DownloadsViewableInternally.js b/browser/components/downloads/test/unit/test_DownloadsViewableInternally.js
new file mode 100644
index 0000000000..07925bc7d5
--- /dev/null
+++ b/browser/components/downloads/test/unit/test_DownloadsViewableInternally.js
@@ -0,0 +1,277 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+const PREF_SVG_DISABLED = "svg.disabled";
+const PREF_WEBP_ENABLED = "image.webp.enabled";
+const PREF_AVIF_ENABLED = "image.avif.enabled";
+const PDF_MIME = "application/pdf";
+const OCTET_MIME = "application/octet-stream";
+const XML_MIME = "text/xml";
+const SVG_MIME = "image/svg+xml";
+const AVIF_MIME = "image/avif";
+const WEBP_MIME = "image/webp";
+
+const { Integration } = ChromeUtils.importESModule(
+  "resource://gre/modules/Integration.sys.mjs"
+);
+const {
+  DownloadsViewableInternally,
+  PREF_ENABLED_TYPES,
+  PREF_BRANCH_WAS_REGISTERED,
+  PREF_BRANCH_PREVIOUS_ACTION,
+  PREF_BRANCH_PREVIOUS_ASK,
+} = ChromeUtils.importESModule(
+  "resource:///modules/DownloadsViewableInternally.sys.mjs"
+);
+
+/* global DownloadIntegration */
+Integration.downloads.defineESModuleGetter(
+  this,
+  "DownloadIntegration",
+  "resource://gre/modules/DownloadIntegration.sys.mjs"
+);
+
+const HandlerService = Cc[
+  "@mozilla.org/uriloader/handler-service;1"
+].getService(Ci.nsIHandlerService);
+const MIMEService = Cc["@mozilla.org/mime;1"].getService(Ci.nsIMIMEService);
+
+function checkPreferInternal(mime, ext, expectedPreferInternal) {
+  const handler = MIMEService.getFromTypeAndExtension(mime, ext);
+  if (expectedPreferInternal) {
+    Assert.equal(
+      handler?.preferredAction,
+      Ci.nsIHandlerInfo.handleInternally,
+      `checking ${mime} preferredAction == handleInternally`
+    );
+  } else {
+    Assert.notEqual(
+      handler?.preferredAction,
+      Ci.nsIHandlerInfo.handleInternally,
+      `checking ${mime} preferredAction != handleInternally`
+    );
+  }
+}
+
+function shouldView(mime, ext) {
+  return DownloadIntegration.shouldViewDownloadInternally(mime, ext);
+}
+
+function checkShouldView(mime, ext, expectedShouldView) {
+  Assert.equal(
+    shouldView(mime, ext),
+    expectedShouldView,
+    `checking ${mime} shouldViewDownloadInternally`
+  );
+}
+
+function checkWasRegistered(ext, expectedWasRegistered) {
+  Assert.equal(
+    Services.prefs.getBoolPref(PREF_BRANCH_WAS_REGISTERED + ext, false),
+    expectedWasRegistered,
+    `checking ${ext} was registered pref`
+  );
+}
+
+function checkAll(mime, ext, expected) {
+  checkPreferInternal(mime, ext, expected && ext != "xml" && ext != "svg");
+  checkShouldView(mime, ext, expected);
+  if (ext != "xml" && ext != "svg") {
+    checkWasRegistered(ext, expected);
+  }
+}
+
+add_task(async function test_viewable_internally() {
+  Services.prefs.setCharPref(PREF_ENABLED_TYPES, "xml , svg,avif,webp");
+  Services.prefs.setBoolPref(PREF_SVG_DISABLED, false);
+  Services.prefs.setBoolPref(PREF_WEBP_ENABLED, true);
+  Services.prefs.setBoolPref(PREF_AVIF_ENABLED, true);
+
+  checkAll(XML_MIME, "xml", false);
+  checkAll(SVG_MIME, "svg", false);
+  checkAll(WEBP_MIME, "webp", false);
+  checkAll(AVIF_MIME, "avif", false);
+
+  DownloadsViewableInternally.register();
+
+  checkAll(XML_MIME, "xml", true);
+  checkAll(SVG_MIME, "svg", true);
+  checkAll(WEBP_MIME, "webp", true);
+  checkAll(AVIF_MIME, "avif", true);
+
+  // Remove webp so it won't be cleared
+  Services.prefs.clearUserPref(PREF_BRANCH_WAS_REGISTERED + "webp");
+
+  // Disable xml, avif and webp, check that avif becomes disabled
+  Services.prefs.setCharPref(PREF_ENABLED_TYPES, "svg");
+
+  // (XML is externally managed, and we just cleared the webp pref)
+  checkAll(XML_MIME, "xml", true);
+  checkPreferInternal(WEBP_MIME, "webp", true);
+
+  // Avif should be disabled
+  checkAll(AVIF_MIME, "avif", false);
+
+  // SVG shouldn't be cleared as it's still enabled
+  checkAll(SVG_MIME, "svg", true);
+
+  Assert.ok(
+    shouldView(PDF_MIME),
+    "application/pdf should be unaffected by pref"
+  );
+  Assert.ok(
+    shouldView(OCTET_MIME, "pdf"),
+    ".pdf should be accepted by extension"
+  );
+  Assert.ok(
+    shouldView(OCTET_MIME, "PDF"),
+    ".pdf should be detected case-insensitively"
+  );
+  Assert.ok(!shouldView(OCTET_MIME, "exe"), ".exe shouldn't be accepted");
+
+  Assert.ok(!shouldView(WEBP_MIME), "imave/webp should be disabled by pref");
+  Assert.ok(!shouldView(AVIF_MIME), "image/avif should be disabled by pref");
+
+  // Enable, check that everything is enabled again
+  Services.prefs.setCharPref(PREF_ENABLED_TYPES, "xml,svg,webp,avif");
+
+  checkAll(XML_MIME, "xml", true);
+  checkAll(SVG_MIME, "svg", true);
+  checkPreferInternal(WEBP_MIME, "webp", true);
+  checkPreferInternal(AVIF_MIME, "avif", true);
+
+  Assert.ok(
+    shouldView(PDF_MIME),
+    "application/pdf should be unaffected by pref"
+  );
+  Assert.ok(shouldView(XML_MIME), "text/xml should be enabled by pref");
+  Assert.ok(
+    shouldView("application/xml"),
+    "alternate MIME type application/xml should be accepted"
+  );
+  Assert.ok(
+    shouldView(OCTET_MIME, "xml"),
+    ".xml should be accepted by extension"
+  );
+
+  // Disable viewable internally, pre-set handlers.
+  Services.prefs.setCharPref(PREF_ENABLED_TYPES, "");
+
+  for (const [mime, ext, action, ask] of [
+    [XML_MIME, "xml", Ci.nsIHandlerInfo.useSystemDefault, true],
+    [SVG_MIME, "svg", Ci.nsIHandlerInfo.saveToDisk, true],
+    [WEBP_MIME, "webp", Ci.nsIHandlerInfo.saveToDisk, false],
+  ]) {
+    let handler = MIMEService.getFromTypeAndExtension(mime, ext);
+    handler.preferredAction = action;
+    handler.alwaysAskBeforeHandling = ask;
+
+    HandlerService.store(handler);
+    checkPreferInternal(mime, ext, false);
+
+    // Expect to read back the same values
+    handler = MIMEService.getFromTypeAndExtension(mime, ext);
+    Assert.equal(handler.preferredAction, action);
+    Assert.equal(handler.alwaysAskBeforeHandling, ask);
+  }
+
+  // Enable viewable internally, SVG and XML should not be replaced, WebP should be saved.
+  Services.prefs.setCharPref(PREF_ENABLED_TYPES, "svg,webp,xml");
+
+  Assert.equal(
+    Services.prefs.prefHasUserValue(PREF_BRANCH_PREVIOUS_ACTION + "svg"),
+    false,
+    "svg action should not be stored"
+  );
+  Assert.equal(
+    Services.prefs.prefHasUserValue(PREF_BRANCH_PREVIOUS_ASK + "svg"),
+    false,
+    "svg ask should not be stored"
+  );
+  Assert.equal(
+    Services.prefs.getIntPref(PREF_BRANCH_PREVIOUS_ACTION + "webp"),
+    Ci.nsIHandlerInfo.saveToDisk,
+    "webp action should be saved"
+  );
+  Assert.equal(
+    Services.prefs.getBoolPref(PREF_BRANCH_PREVIOUS_ASK + "webp"),
+    false,
+    "webp ask should be saved"
+  );
+
+  {
+    let handler = MIMEService.getFromTypeAndExtension(SVG_MIME, "svg");
+    Assert.equal(
+      handler.preferredAction,
+      Ci.nsIHandlerInfo.saveToDisk,
+      "svg action should be preserved"
+    );
+    Assert.equal(
+      !!handler.alwaysAskBeforeHandling,
+      true,
+      "svg ask should be preserved"
+    );
+    // Clean up
+    HandlerService.remove(handler);
+    handler = MIMEService.getFromTypeAndExtension(XML_MIME, "xml");
+    Assert.equal(
+      handler.preferredAction,
+      Ci.nsIHandlerInfo.useSystemDefault,
+      "xml action should be preserved"
+    );
+    Assert.equal(
+      !!handler.alwaysAskBeforeHandling,
+      true,
+      "xml ask should be preserved"
+    );
+    // Clean up
+    HandlerService.remove(handler);
+  }
+  // It should still be possible to view XML internally
+  checkShouldView(XML_MIME, "xml", true);
+
+  checkAll(SVG_MIME, "svg", true);
+  checkAll(WEBP_MIME, "webp", true);
+
+  // Disable SVG to test SVG enabled check (depends on the pref)
+  Services.prefs.setBoolPref(PREF_SVG_DISABLED, true);
+  checkAll(SVG_MIME, "svg", false);
+  Services.prefs.setBoolPref(PREF_SVG_DISABLED, false);
+  {
+    let handler = MIMEService.getFromTypeAndExtension(SVG_MIME, "svg");
+    handler.preferredAction = Ci.nsIHandlerInfo.saveToDisk;
+    handler.alwaysAskBeforeHandling = false;
+    HandlerService.store(handler);
+  }
+
+  checkAll(SVG_MIME, "svg", true);
+
+  // Test WebP enabled check (depends on the pref)
+  Services.prefs.setBoolPref(PREF_WEBP_ENABLED, false);
+  // Should have restored the settings from above
+  {
+    let handler = MIMEService.getFromTypeAndExtension(WEBP_MIME, "webp");
+    Assert.equal(handler.preferredAction, Ci.nsIHandlerInfo.saveToDisk);
+    Assert.equal(!!handler.alwaysAskBeforeHandling, false);
+    // Clean up
+    HandlerService.remove(handler);
+  }
+  checkAll(WEBP_MIME, "webp", false);
+
+  Services.prefs.setBoolPref(PREF_WEBP_ENABLED, true);
+  checkAll(WEBP_MIME, "webp", true);
+
+  Assert.ok(!shouldView(null, "pdf"), "missing MIME shouldn't be accepted");
+  Assert.ok(!shouldView(null, "xml"), "missing MIME shouldn't be accepted");
+  Assert.ok(!shouldView(OCTET_MIME), "unsupported MIME shouldn't be accepted");
+  Assert.ok(!shouldView(OCTET_MIME, "exe"), ".exe shouldn't be accepted");
+});
+
+registerCleanupFunction(() => {
+  // Clear all types to remove any saved values
+  Services.prefs.setCharPref(PREF_ENABLED_TYPES, "");
+  // Reset to the defaults
+  Services.prefs.clearUserPref(PREF_ENABLED_TYPES);
+  Services.prefs.clearUserPref(PREF_SVG_DISABLED);
+  Services.prefs.clearUserPref(PREF_WEBP_ENABLED);
+});
diff --git a/browser/components/downloads/test/unit/xpcshell.ini b/browser/components/downloads/test/unit/xpcshell.ini
new file mode 100644
index 0000000000..53087b4b82
--- /dev/null
+++ b/browser/components/downloads/test/unit/xpcshell.ini
@@ -0,0 +1,9 @@
+[DEFAULT]
+head = head.js
+firefox-appdir = browser
+skip-if = toolkit == 'android' # bug 1730213
+
+
+[test_DownloadsCommon_getMimeInfo.js]
+[test_DownloadsCommon_isFileOfType.js]
+[test_DownloadsViewableInternally.js]