diff --git a/browser/base/content/test/tabPrompts/browser_contentOrigins.js b/browser/base/content/test/tabPrompts/browser_contentOrigins.js
index 4a93fa3ab97f..c7eda34cf6ce 100644
--- a/browser/base/content/test/tabPrompts/browser_contentOrigins.js
+++ b/browser/base/content/test/tabPrompts/browser_contentOrigins.js
@@ -137,8 +137,6 @@ async function checkDialog(
 add_task(async function setup() {
   await SpecialPowers.pushPrefEnv({
     set: [
-      ["browser.proton.enabled", true],
-      ["browser.proton.modals.enabled", true],
       ["prompts.contentPromptSubDialog", true],
       ["prompts.modalType.httpAuth", Ci.nsIPrompt.MODAL_TYPE_TAB],
       ["prompts.tabChromePromptSubDialog", true],
diff --git a/browser/base/content/test/tabdialogs/browser_tabdialogbox_content_prompts.js b/browser/base/content/test/tabdialogs/browser_tabdialogbox_content_prompts.js
index bb35b9ea0276..f0d2b4f42931 100644
--- a/browser/base/content/test/tabdialogs/browser_tabdialogbox_content_prompts.js
+++ b/browser/base/content/test/tabdialogs/browser_tabdialogbox_content_prompts.js
@@ -91,7 +91,7 @@ add_task(async function test_tabdialog_null_principal_title() {
   await BrowserTestUtils.withNewTab(TEST_DATA_URI, async function(browser) {
     info("Waiting for dialog to open.");
     await dialogShown;
-    await checkOriginText(browser, "ScriptDlgNullPrincipalHeading");
+    await checkOriginText(browser);
   });
 });
 
@@ -111,7 +111,7 @@ add_task(async function test_tabdialog_extension_title() {
   await BrowserTestUtils.withNewTab(url, async function(browser) {
     info("Waiting for dialog to open.");
     await dialogShown;
-    await checkOriginText(browser, "ScriptDlgHeading", "Test Extension");
+    await checkOriginText(browser, "Test Extension");
   });
 
   await extension.unload();
@@ -129,7 +129,7 @@ add_task(async function test_tabdialog_page_title() {
   await BrowserTestUtils.withNewTab(TEST_PAGE, async function(browser) {
     info("Waiting for dialog to open.");
     await dialogShown;
-    await checkOriginText(browser, "ScriptDlgHeading", TEST_ORIGIN);
+    await checkOriginText(browser, TEST_ORIGIN);
   });
 });
 
@@ -138,12 +138,10 @@ add_task(async function test_tabdialog_page_title() {
  *
  * @param {Object} browser
  *        The browser the dialog was opened from.
- * @param {String}  stringKey
- *        The bundle key for the text that should be displayed.
  * @param {String|null}  origin
  *        The page origin that should be displayed in the header, if any.
  */
-async function checkOriginText(browser, stringKey, origin = null) {
+async function checkOriginText(browser, origin = null) {
   info("Check the title is visible.");
   let dialogBox = gBrowser.getTabDialogBox(browser);
   let contentPromptManager = dialogBox.getContentDialogManager();
@@ -153,39 +151,24 @@ async function checkOriginText(browser, stringKey, origin = null) {
   await dialog._dialogReady;
 
   let dialogDoc = dialog._frame.contentWindow.document;
-  let protonModals = Services.prefs.getBoolPref(
-    "browser.proton.modals.enabled",
-    false
-  );
-  let titleSelector = protonModals ? "#titleText" : "#infoTitle";
+  let titleSelector = "#titleText";
   let infoTitle = dialogDoc.querySelector(titleSelector);
   ok(BrowserTestUtils.is_visible(infoTitle), "Title text is visible");
 
   info("Check the displayed origin text is correct.");
-  let titleText;
-
-  if (protonModals) {
-    if (origin) {
-      let host = origin;
-      try {
-        host = new URL(origin).host;
-      } catch (ex) {
-        /* will fail for the extension case. */
-      }
-      is(infoTitle.textContent, host, "Origin should be in header.");
-    } else {
-      is(
-        infoTitle.dataset.l10nId,
-        "common-dialog-title-null",
-        "Null principal string should be in header."
-      );
+  if (origin) {
+    let host = origin;
+    try {
+      host = new URL(origin).host;
+    } catch (ex) {
+      /* will fail for the extension case. */
     }
+    is(infoTitle.textContent, host, "Origin should be in header.");
   } else {
-    if (origin) {
-      titleText = commonDialogsBundle.formatStringFromName(stringKey, [origin]);
-    } else {
-      titleText = commonDialogsBundle.GetStringFromName(stringKey);
-    }
-    is(infoTitle.textContent, titleText, "Origin header is correct.");
+    is(
+      infoTitle.dataset.l10nId,
+      "common-dialog-title-null",
+      "Null principal string should be in header."
+    );
   }
 }
diff --git a/browser/components/customizableui/test/browser_981305_separator_insertion.js b/browser/components/customizableui/test/browser_981305_separator_insertion.js
index db6c9d4e50b1..77deec0d3bec 100644
--- a/browser/components/customizableui/test/browser_981305_separator_insertion.js
+++ b/browser/components/customizableui/test/browser_981305_separator_insertion.js
@@ -72,10 +72,7 @@ async function checkSeparatorInsertion(menuId, buttonId, subviewId) {
 }
 
 add_task(async function check_devtools_separator() {
-  const protonEnabled =
-    Services.prefs.getBoolPref("browser.proton.doorhangers.enabled", false) &&
-    Services.prefs.getBoolPref("browser.proton.enabled", false);
-  const panelviewId = protonEnabled ? "appmenu-moreTools" : "PanelUI-developer";
+  const panelviewId = "appmenu-moreTools";
 
   await checkSeparatorInsertion(
     "menuWebDeveloperPopup",
diff --git a/browser/components/customizableui/test/browser_proton_moreTools_panel.js b/browser/components/customizableui/test/browser_proton_moreTools_panel.js
index 097b1b4c22f9..7955a83d0e72 100644
--- a/browser/components/customizableui/test/browser_proton_moreTools_panel.js
+++ b/browser/components/customizableui/test/browser_proton_moreTools_panel.js
@@ -14,15 +14,8 @@ add_task(async function testMoreToolsPanelInToolbar() {
   // We need to force DevToolsStartup to rebuild the developer tool toggle so that
   // proton prefs are applied to the new browser window for this test.
   DevToolsStartup.developerToggleCreated = false;
-  await SpecialPowers.pushPrefEnv({
-    set: [
-      ["browser.proton.enabled", true],
-      ["browser.proton.doorhangers.enabled", true],
-    ],
-  });
   CustomizableUI.destroyWidget("developer-button");
 
-  // Now open a new window where the proton prefs will be applied.
   const win = await BrowserTestUtils.openNewBrowserWindow();
 
   CustomizableUI.addWidgetToArea(
diff --git a/browser/components/fxmonitor/moz.build b/browser/components/fxmonitor/moz.build
index 1315cd4f5b07..863aacf1031b 100644
--- a/browser/components/fxmonitor/moz.build
+++ b/browser/components/fxmonitor/moz.build
@@ -12,5 +12,3 @@ EXTRA_JS_MODULES += [
 ]
 
 JAR_MANIFESTS += ["jar.mn"]
-
-BROWSER_CHROME_MANIFESTS += ["test/browser/browser.ini"]
diff --git a/browser/components/fxmonitor/test/browser/browser.ini b/browser/components/fxmonitor/test/browser/browser.ini
deleted file mode 100644
index 613bd0e1af6b..000000000000
--- a/browser/components/fxmonitor/test/browser/browser.ini
+++ /dev/null
@@ -1,3 +0,0 @@
-[browser_fxmonitor_doorhanger.js]
-skip-if = debug # bug 1547517
-tags = remote-settings
diff --git a/browser/components/fxmonitor/test/browser/browser_fxmonitor_doorhanger.js b/browser/components/fxmonitor/test/browser/browser_fxmonitor_doorhanger.js
deleted file mode 100644
index 246e97e4f614..000000000000
--- a/browser/components/fxmonitor/test/browser/browser_fxmonitor_doorhanger.js
+++ /dev/null
@@ -1,339 +0,0 @@
-"use strict";
-
-ChromeUtils.defineModuleGetter(
-  this,
-  "AddonManager",
-  "resource://gre/modules/AddonManager.jsm"
-);
-ChromeUtils.defineModuleGetter(
-  this,
-  "RemoteSettings",
-  "resource://services-settings/remote-settings.js"
-);
-
-const kNotificationId = "fxmonitor";
-const kRemoteSettingsKey = "fxmonitor-breaches";
-
-async function fxmonitorNotificationShown() {
-  await TestUtils.waitForCondition(() => {
-    return (
-      PopupNotifications.getNotification(kNotificationId) &&
-      PopupNotifications.panel.state == "open"
-    );
-  }, "Waiting for fxmonitor notification to be shown");
-  ok(true, "Firefox Monitor PopupNotification was added.");
-}
-
-async function fxmonitorNotificationGone() {
-  await TestUtils.waitForCondition(() => {
-    return (
-      !PopupNotifications.getNotification(kNotificationId) &&
-      PopupNotifications.panel.state == "closed"
-    );
-  }, "Waiting for fxmonitor notification to go away");
-  ok(true, "Firefox Monitor PopupNotification was removed.");
-}
-
-let cps2 = Cc["@mozilla.org/content-pref/service;1"].getService(
-  Ci.nsIContentPrefService2
-);
-
-async function clearWarnedHosts() {
-  return new Promise((resolve, reject) => {
-    cps2.removeByName(
-      "extensions.fxmonitor.hostAlreadyWarned",
-      Cu.createLoadContext(),
-      {
-        handleCompletion: resolve,
-      }
-    );
-  });
-}
-
-add_task(async function setup() {
-  // This test used to rely on the initial timer of
-  // TestUtils.waitForCondition. See bug 1700683.
-  let originalWaitForCondition = TestUtils.waitForCondition;
-  TestUtils.waitForCondition = async function(
-    condition,
-    msg,
-    interval = 100,
-    maxTries = 50
-  ) {
-    // eslint-disable-next-line mozilla/no-arbitrary-setTimeout
-    await new Promise(resolve => setTimeout(resolve, 100));
-
-    return originalWaitForCondition(condition, msg, interval, maxTries);
-  };
-  registerCleanupFunction(function() {
-    TestUtils.waitForCondition = originalWaitForCondition;
-  });
-
-  // Disable Proton. The Firefox Monitor doorhanger is disabled with Proton
-  // enabled, so most of these tests won't work in that configuration. We are,
-  // however, keeping these tests around for now until Proton ships.
-  //
-  // There is a test later in this file that checks that the panel doesn't appear
-  // with Proton enabled.
-  await SpecialPowers.pushPrefEnv({
-    set: [["browser.proton.doorhangers.enabled", false]],
-  });
-});
-
-add_task(async function test_main_flow() {
-  info("Test that we show the first alert correctly for a recent breach.");
-
-  // Pre-populate the Remote Settings collection with a breach.
-  let db = await RemoteSettings(kRemoteSettingsKey).db;
-  let BreachDate = new Date();
-  let AddedDate = new Date();
-  await db.create({
-    Domain: "example.com",
-    Name: "Example Site",
-    BreachDate: `${BreachDate.getFullYear()}-${BreachDate.getMonth() +
-      1}-${BreachDate.getDate()}`,
-    AddedDate: `${AddedDate.getFullYear()}-${AddedDate.getMonth() +
-      1}-${AddedDate.getDate()}`,
-    PwnCount: 1000000,
-  });
-  await db.importChanges({}, 1234567);
-
-  // Trigger a sync.
-  await RemoteSettings(kRemoteSettingsKey).emit("sync", {
-    data: {
-      current: await RemoteSettings(kRemoteSettingsKey).get(),
-    },
-  });
-
-  // Enable the extension.
-  await SpecialPowers.pushPrefEnv({
-    set: [["extensions.fxmonitor.FirefoxMonitorURL", "http://example.org"]],
-  });
-
-  // Open a tab and wait for the alert.
-  let tab = await BrowserTestUtils.openNewForegroundTab(
-    gBrowser,
-    "http://example.com"
-  );
-  await fxmonitorNotificationShown();
-
-  // Test that dismissing works.
-  let notification = Array.prototype.find.call(
-    PopupNotifications.panel.children,
-    elt => elt.getAttribute("popupid") == kNotificationId
-  );
-  EventUtils.synthesizeMouseAtCenter(notification.secondaryButton, {});
-  await fxmonitorNotificationGone();
-
-  // Reload and make sure the alert isn't shown again.
-  let promise = BrowserTestUtils.browserLoaded(tab.linkedBrowser);
-  tab.linkedBrowser.reload();
-  await promise;
-  await fxmonitorNotificationGone();
-
-  // Reset state.
-  await db.clear();
-  await db.importChanges({}, 1234567);
-  await clearWarnedHosts();
-  await SpecialPowers.pushPrefEnv({
-    clear: [["extensions.fxmonitor.firstAlertShown"]],
-  });
-
-  // Reload and wait for the alert.
-  promise = BrowserTestUtils.browserLoaded(tab.linkedBrowser);
-  tab.linkedBrowser.reload();
-  await promise;
-  await fxmonitorNotificationShown();
-
-  // Test that the primary button opens Firefox Monitor in a new tab.
-  notification = Array.prototype.find.call(
-    PopupNotifications.panel.children,
-    elt => elt.getAttribute("popupid") == kNotificationId
-  );
-  let url = `http://example.org/?breach=${encodeURIComponent(
-    "Example Site"
-  )}&utm_source=firefox&utm_medium=popup`;
-  promise = BrowserTestUtils.waitForNewTab(gBrowser, url);
-  EventUtils.synthesizeMouseAtCenter(notification.button, {});
-  let newtab = await promise;
-
-  // Close the new tab and check that the alert is gone.
-  BrowserTestUtils.removeTab(newtab);
-  await fxmonitorNotificationGone();
-
-  // Reset state (but not firstAlertShown).
-  await db.clear();
-  await db.importChanges({}, 1234567);
-  await clearWarnedHosts();
-
-  info(
-    "Test that we do not show the second alert for a breach added over two months ago."
-  );
-
-  // Add a new "old" breach - added over 2 months ago.
-  AddedDate.setMonth(AddedDate.getMonth() - 3);
-  await db.create({
-    Domain: "example.com",
-    Name: "Example Site",
-    BreachDate: `${BreachDate.getFullYear()}-${BreachDate.getMonth() +
-      1}-${BreachDate.getDate()}`,
-    AddedDate: `${AddedDate.getFullYear()}-${AddedDate.getMonth() +
-      1}-${AddedDate.getDate()}`,
-    PwnCount: 1000000,
-  });
-  await db.importChanges({}, 1234567);
-
-  // Trigger a sync.
-  await RemoteSettings(kRemoteSettingsKey).emit("sync", {
-    data: {
-      current: await RemoteSettings(kRemoteSettingsKey).get(),
-    },
-  });
-
-  // Check that there's no alert for the old breach.
-  promise = BrowserTestUtils.browserLoaded(tab.linkedBrowser);
-  tab.linkedBrowser.reload();
-  await promise;
-  await fxmonitorNotificationGone();
-
-  // Reset state (but not firstAlertShown).
-  AddedDate.setMonth(AddedDate.getMonth() + 3);
-  await db.clear();
-  await db.importChanges({}, 1234567);
-  await clearWarnedHosts();
-
-  info("Test that we do show the second alert for a recent breach.");
-
-  // Add a new "recent" breach.
-  await db.create({
-    Domain: "example.com",
-    Name: "Example Site",
-    BreachDate: `${BreachDate.getFullYear()}-${BreachDate.getMonth() +
-      1}-${BreachDate.getDate()}`,
-    AddedDate: `${AddedDate.getFullYear()}-${AddedDate.getMonth() +
-      1}-${AddedDate.getDate()}`,
-    PwnCount: 1000000,
-  });
-  await db.importChanges({}, 1234567);
-
-  // Trigger a sync.
-  await RemoteSettings(kRemoteSettingsKey).emit("sync", {
-    data: {
-      current: await RemoteSettings(kRemoteSettingsKey).get(),
-    },
-  });
-
-  // Check that there's an alert for the new breach.
-  promise = BrowserTestUtils.browserLoaded(tab.linkedBrowser);
-  tab.linkedBrowser.reload();
-  await promise;
-  await fxmonitorNotificationShown();
-
-  // Reset state (including firstAlertShown)
-  await db.clear();
-  await db.importChanges({}, 1234567);
-  await clearWarnedHosts();
-  await SpecialPowers.pushPrefEnv({
-    clear: [["extensions.fxmonitor.firstAlertShown"]],
-  });
-
-  info(
-    "Test that we do not show the first alert for a breach added over a year ago."
-  );
-
-  // Add a new "old" breach - added over a year ago.
-  AddedDate.setFullYear(AddedDate.getFullYear() - 2);
-  await db.create({
-    Domain: "example.com",
-    Name: "Example Site",
-    BreachDate: `${BreachDate.getFullYear()}-${BreachDate.getMonth() +
-      1}-${BreachDate.getDate()}`,
-    AddedDate: `${AddedDate.getFullYear()}-${AddedDate.getMonth() +
-      1}-${AddedDate.getDate()}`,
-    PwnCount: 1000000,
-  });
-  await db.importChanges({}, 1234567);
-
-  // Trigger a sync.
-  await RemoteSettings(kRemoteSettingsKey).emit("sync", {
-    data: {
-      current: await RemoteSettings(kRemoteSettingsKey).get(),
-    },
-  });
-
-  // Check that there's no alert for the old breach.
-  promise = BrowserTestUtils.browserLoaded(tab.linkedBrowser);
-  tab.linkedBrowser.reload();
-  await promise;
-  await fxmonitorNotificationGone();
-
-  // Clean up.
-  BrowserTestUtils.removeTab(tab);
-  await db.clear();
-  await db.importChanges({}, 1234567);
-  // Trigger a sync to clear.
-  await RemoteSettings(kRemoteSettingsKey).emit("sync", {
-    data: {
-      current: [],
-    },
-  });
-  await clearWarnedHosts();
-  await SpecialPowers.pushPrefEnv({
-    clear: [["extensions.fxmonitor.firstAlertShown"]],
-  });
-});
-
-add_task(async function test_proton_disabled() {
-  info("Test that we don't show an alert if proton is enabled.");
-
-  // Pre-populate the Remote Settings collection with a breach.
-  let db = await RemoteSettings(kRemoteSettingsKey).db;
-  let BreachDate = new Date();
-  let AddedDate = new Date();
-  await db.create({
-    Domain: "example.com",
-    Name: "Example Site",
-    BreachDate: `${BreachDate.getFullYear()}-${BreachDate.getMonth() +
-      1}-${BreachDate.getDate()}`,
-    AddedDate: `${AddedDate.getFullYear()}-${AddedDate.getMonth() +
-      1}-${AddedDate.getDate()}`,
-    PwnCount: 1000000,
-  });
-  await db.importChanges({}, 1234567);
-
-  // Trigger a sync.
-  await RemoteSettings(kRemoteSettingsKey).emit("sync", {
-    data: {
-      current: await RemoteSettings(kRemoteSettingsKey).get(),
-    },
-  });
-
-  // Enable proton
-  await SpecialPowers.pushPrefEnv({
-    set: [["browser.proton.doorhangers.enabled", true]],
-  });
-
-  // Open a tab and wait for the alert.
-  let tab = await BrowserTestUtils.openNewForegroundTab(
-    gBrowser,
-    "http://example.com"
-  );
-
-  try {
-    await fxmonitorNotificationShown();
-    ok(false, "Notification was shown but shouldn't have been!");
-  } catch (e) {
-    ok(true, "No notifaction was shown with proton enabled.");
-  }
-
-  // Clean up.
-  BrowserTestUtils.removeTab(tab);
-  await db.clear();
-  await db.importChanges({}, 1234567);
-  // Trigger a sync to clear.
-  await RemoteSettings(kRemoteSettingsKey).emit("sync", {
-    data: {
-      current: [],
-    },
-  });
-});
diff --git a/browser/components/places/tests/browser/browser_bookmarksProperties.js b/browser/components/places/tests/browser/browser_bookmarksProperties.js
index 5e91ca3d27fc..ada68df61a87 100644
--- a/browser/components/places/tests/browser/browser_bookmarksProperties.js
+++ b/browser/components/places/tests/browser/browser_bookmarksProperties.js
@@ -470,12 +470,8 @@ function execute_test_in_sidebar(test) {
 }
 
 async function promise_properties_window(dialogUrl = DIALOG_URL) {
-  let protonModal = Services.prefs.getBoolPref(
-    "browser.proton.modals.enabled",
-    false
-  );
   let win = await BrowserTestUtils.promiseAlertDialogOpen(null, dialogUrl, {
-    isSubDialog: protonModal,
+    isSubDialog: true,
   });
   await SimpleTest.promiseFocus(win);
   await TestUtils.waitForCondition(
diff --git a/browser/components/places/tests/browser/head.js b/browser/components/places/tests/browser/head.js
index c8803267e93f..1831d44746da 100644
--- a/browser/components/places/tests/browser/head.js
+++ b/browser/components/places/tests/browser/head.js
@@ -214,13 +214,11 @@ var withBookmarksDialog = async function(
   skipOverlayWait = false
 ) {
   let closed = false;
-  let protonModal =
-    Services.prefs.getBoolPref("browser.proton.modals.enabled", false) &&
-    // We can't show the in-window prompt for windows which don't have
-    // gDialogBox, like the library (Places:Organizer) window.
-    Services.wm.getMostRecentWindow("").gDialogBox;
+  // We can't show the in-window prompt for windows which don't have
+  // gDialogBox, like the library (Places:Organizer) window.
+  let hasDialogBox = !!Services.wm.getMostRecentWindow("").gDialogBox;
   let dialogPromise;
-  if (protonModal) {
+  if (hasDialogBox) {
     dialogPromise = BrowserTestUtils.promiseAlertDialogOpen(null, dialogUrl, {
       isSubDialog: true,
     });
@@ -237,7 +235,7 @@ var withBookmarksDialog = async function(
     });
   }
   let dialogClosePromise = dialogPromise.then(win => {
-    if (!protonModal) {
+    if (!hasDialogBox) {
       return BrowserTestUtils.domWindowClosed(win);
     }
     let container = win.top.document.getElementById("window-modal-dialog");
diff --git a/toolkit/components/passwordmgr/test/browser/browser_basicAuth_multiTab.js b/toolkit/components/passwordmgr/test/browser/browser_basicAuth_multiTab.js
index 2b34210e3b77..4e73e269e52c 100644
--- a/toolkit/components/passwordmgr/test/browser/browser_basicAuth_multiTab.js
+++ b/toolkit/components/passwordmgr/test/browser/browser_basicAuth_multiTab.js
@@ -112,22 +112,13 @@ add_task(async function test() {
 
   is(prompts.length, tabs.length, "Should have one prompt per tab");
 
-  if (Services.prefs.getBoolPref("browser.proton.modals.enabled", false)) {
-    for (let i = 0; i < prompts.length; i++) {
-      let titleEl = prompts[i].ui.prompt.document.querySelector("#titleText");
-      is(
-        titleEl.textContent,
-        new URL(tabs[i].origin).host,
-        "Prompt matches the tab's host"
-      );
-    }
-  } else {
-    for (let i = 0; i < prompts.length; i++) {
-      ok(
-        prompts[i].args.text.startsWith(tabs[i].origin),
-        "Prompt matches the tabs origin"
-      );
-    }
+  for (let i = 0; i < prompts.length; i++) {
+    let titleEl = prompts[i].ui.prompt.document.querySelector("#titleText");
+    is(
+      titleEl.textContent,
+      new URL(tabs[i].origin).host,
+      "Prompt matches the tab's host"
+    );
   }
 
   // Interact with the prompts. This is deliberately done out of order