--- a/browser/base/content/browser-commands.js
+++ b/browser/base/content/browser-commands.js
@@ -373,9 +373,45 @@ var BrowserCommands = {
           nsIFilePicker.filterXML |
           nsIFilePicker.filterHTML |
           nsIFilePicker.filterPDF
       );
       fp.displayDirectory = gLastOpenDirectory.path;
       fp.open(fpCallback);
     } catch (ex) {}
   },
+
+  closeTabOrWindow(event) {
+    // If we're not a browser window, just close the window.
+    if (window.location.href != AppConstants.BROWSER_CHROME_URL) {
+      closeWindow(true);
+      return;
+    }
+
+    // In a multi-select context, close all selected tabs
+    if (gBrowser.multiSelectedTabsCount) {
+      gBrowser.removeMultiSelectedTabs();
+      return;
+    }
+
+    // Keyboard shortcuts that would close a tab that is pinned select the first
+    // unpinned tab instead.
+    if (
+      event &&
+      (event.ctrlKey || event.metaKey || event.altKey) &&
+      gBrowser.selectedTab.pinned
+    ) {
+      if (gBrowser.visibleTabs.length > gBrowser._numPinnedTabs) {
+        gBrowser.tabContainer.selectedIndex = gBrowser._numPinnedTabs;
+      }
+      return;
+    }
+
+    // If the current tab is the last one, this will close the window.
+    gBrowser.removeCurrentTab({ animate: true });
+  },
+
+  tryToCloseWindow(event) {
+    if (WindowIsClosing(event)) {
+      window.close();
+    } // WindowIsClosing does all the necessary checks
+  },
 };

--- a/browser/base/content/browser-sets.inc
+++ b/browser/base/content/browser-sets.inc
@@ -27,18 +27,18 @@
     <command id="Browser:SendLink"
              oncommand="MailIntegration.sendLinkForBrowser(gBrowser.selectedBrowser);"/>
 
     <command id="cmd_pageSetup" oncommand="PrintUtils.showPageSetup();"/>
     <command id="cmd_print" oncommand="PrintUtils.startPrintWindow(gBrowser.selectedBrowser.browsingContext);"/>
     <command id="cmd_printPreviewToggle" oncommand="PrintUtils.togglePrintPreview(gBrowser.selectedBrowser.browsingContext);"/>
     <command id="cmd_file_importFromAnotherBrowser" oncommand="MigrationUtils.showMigrationWizard(window, { entrypoint: MigrationUtils.MIGRATION_ENTRYPOINTS.FILE_MENU });"/>
     <command id="cmd_help_importFromAnotherBrowser" oncommand="MigrationUtils.showMigrationWizard(window, { entrypoint: MigrationUtils.MIGRATION_ENTRYPOINTS.HELP_MENU });"/>
-    <command id="cmd_close" oncommand="BrowserCloseTabOrWindow(event);"/>
-    <command id="cmd_closeWindow" oncommand="BrowserTryToCloseWindow(event)"/>
+    <command id="cmd_close" oncommand="BrowserCommands.closeTabOrWindow(event);"/>
+    <command id="cmd_closeWindow" oncommand="BrowserCommands.tryToCloseWindow(event)"/>
     <command id="cmd_toggleMute" oncommand="gBrowser.toggleMuteAudioOnMultiSelectedTabs(gBrowser.selectedTab)"/>
     <command id="cmd_CustomizeToolbars" oncommand="gCustomizeMode.enter()"/>
     <command id="cmd_toggleOfflineStatus" oncommand="BrowserOffline.toggleOfflineStatus();"/>
     <command id="cmd_quitApplication" oncommand="goQuitApplication(event)"/>
 
     <command id="View:AboutProcesses" oncommand="switchToTabHavingURI('about:processes', true)"/>
     <command id="View:PageSource" oncommand="BrowserViewSource(window.gBrowser.selectedBrowser);"/>
     <command id="View:PageInfo" oncommand="BrowserPageInfo();"/>

--- a/browser/base/content/browser.js
+++ b/browser/base/content/browser.js
@@ -2645,17 +2645,17 @@ function HandleAppCommandEvent(evt) {
       break;
     case "Home":
       BrowserCommands.home();
       break;
     case "New":
       BrowserCommands.openTab();
       break;
     case "Close":
-      BrowserCloseTabOrWindow();
+      BrowserCommands.closeTabOrWindow();
       break;
     case "Find":
       gLazyFindCommand("onFindCommand");
       break;
     case "Help":
       openHelpLink("firefox-help");
       break;
     case "Open":
@@ -2760,52 +2760,16 @@ var gLastOpenDirectory = {
       );
     }
   },
   reset() {
     this._lastDir = null;
   },
 };
 
-function BrowserCloseTabOrWindow(event) {
-  // If we're not a browser window, just close the window.
-  if (window.location.href != AppConstants.BROWSER_CHROME_URL) {
-    closeWindow(true);
-    return;
-  }
-
-  // In a multi-select context, close all selected tabs
-  if (gBrowser.multiSelectedTabsCount) {
-    gBrowser.removeMultiSelectedTabs();
-    return;
-  }
-
-  // Keyboard shortcuts that would close a tab that is pinned select the first
-  // unpinned tab instead.
-  if (
-    event &&
-    (event.ctrlKey || event.metaKey || event.altKey) &&
-    gBrowser.selectedTab.pinned
-  ) {
-    if (gBrowser.visibleTabs.length > gBrowser._numPinnedTabs) {
-      gBrowser.tabContainer.selectedIndex = gBrowser._numPinnedTabs;
-    }
-    return;
-  }
-
-  // If the current tab is the last one, this will close the window.
-  gBrowser.removeCurrentTab({ animate: true });
-}
-
-function BrowserTryToCloseWindow(event) {
-  if (WindowIsClosing(event)) {
-    window.close();
-  } // WindowIsClosing does all the necessary checks
-}
-
 function getLoadContext() {
   return window.docShell.QueryInterface(Ci.nsILoadContext);
 }
 
 function readFromClipboard() {
   var url;
 
   try {

--- a/browser/base/content/browser.js.globals
+++ b/browser/base/content/browser.js.globals
@@ -32,18 +32,16 @@
   "delayedStartupPromise",
   "gBrowserInit",
   "HandleAppCommandEvent",
   "BrowserCommands",
   "kSkipCacheFlags",
   "loadOneOrMoreURIs",
   "openLocation",
   "gLastOpenDirectory",
-  "BrowserCloseTabOrWindow",
-  "BrowserTryToCloseWindow",
   "getLoadContext",
   "readFromClipboard",
   "BrowserViewSourceOfDocument",
   "BrowserViewSource",
   "BrowserPageInfo",
   "UpdateUrlbarSearchSplitterState",
   "UpdatePopupNotificationsVisibility",
   "PageProxyClickHandler",

--- a/browser/base/content/test/general/browser_beforeunload_duplicate_dialogs.js
+++ b/browser/base/content/test/general/browser_beforeunload_duplicate_dialogs.js
@@ -52,17 +52,17 @@ add_task(async function closeWindowWithM
   await promiseTabLoadEvent(firstTab, TEST_PAGE);
   await promiseTabLoadEvent(
     BrowserTestUtils.addTab(newWin.gBrowser),
     // eslint-disable-next-line @microsoft/sdl/no-insecure-url
     "http://example.com/"
   );
   let windowClosedPromise = BrowserTestUtils.domWindowClosed(newWin);
   expectingDialog = true;
-  newWin.BrowserTryToCloseWindow();
+  newWin.BrowserCommands.tryToCloseWindow();
   await windowClosedPromise;
   ok(!expectingDialog, "There should have been a dialog.");
   ok(newWin.closed, "Window should be closed.");
   Services.prefs.clearUserPref("browser.tabs.warnOnClose");
 });
 
 add_task(async function closeWindoWithSingleTabTwice() {
   let newWin = await promiseOpenAndLoadWindow({}, true);

--- a/browser/base/content/test/general/browser_private_no_prompt.js
+++ b/browser/base/content/test/general/browser_private_no_prompt.js
@@ -1,12 +1,12 @@
 function test() {
   waitForExplicitFinish();
   var privateWin = OpenBrowserWindow({ private: true });
 
   whenDelayedStartupFinished(privateWin, function () {
     privateWin.BrowserCommands.openTab();
-    privateWin.BrowserTryToCloseWindow();
+    privateWin.BrowserCommands.tryToCloseWindow();
     ok(true, "didn't prompt");
 
     executeSoon(finish);
   });
 }

--- a/browser/base/content/test/popups/browser_popup_close_main_window.js
+++ b/browser/base/content/test/popups/browser_popup_close_main_window.js
@@ -32,17 +32,17 @@ add_task(async function closing_last_win
 
   let observed = 0;
   function obs() {
     observed++;
   }
   Services.obs.addObserver(obs, "browser-lastwindow-close-requested");
   let newWin = await BrowserTestUtils.openNewBrowserWindow();
   let closedPromise = BrowserTestUtils.windowClosed(newWin);
-  newWin.BrowserTryToCloseWindow();
+  newWin.BrowserCommands.tryToCloseWindow();
   await closedPromise;
   is(observed, 1, "Got a notification for closing the normal window.");
   Services.obs.removeObserver(obs, "browser-lastwindow-close-requested");
 });
 
 /**
  * Check that if we close the 1 remaining window and also have a popup open,
  * we don't treat it as quitting.
@@ -63,22 +63,22 @@ add_task(async function closing_last_win
   Services.obs.addObserver(obs, "browser-lastwindow-close-requested");
   let newWin = await BrowserTestUtils.openNewBrowserWindow();
   let popupPromise = BrowserTestUtils.waitForNewWindow("https://example.com/");
   SpecialPowers.spawn(newWin.gBrowser.selectedBrowser, [], function () {
     content.open("https://example.com/", "_blank", "height=500");
   });
   let popupWin = await popupPromise;
   let closedPromise = BrowserTestUtils.windowClosed(newWin);
-  newWin.BrowserTryToCloseWindow();
+  newWin.BrowserCommands.tryToCloseWindow();
   await closedPromise;
   is(observed, 0, "Got no notification for closing the normal window.");
 
   closedPromise = BrowserTestUtils.windowClosed(popupWin);
-  popupWin.BrowserTryToCloseWindow();
+  popupWin.BrowserCommands.tryToCloseWindow();
   await closedPromise;
   is(
     observed,
     0,
     "Got no notification now that we're closing the last window, as it's a popup."
   );
   Services.obs.removeObserver(obs, "browser-lastwindow-close-requested");
 });

--- a/browser/components/firefoxview/tests/browser/browser_tab_on_close_warning.js
+++ b/browser/components/firefoxview/tests/browser/browser_tab_on_close_warning.js
@@ -26,17 +26,17 @@ add_task(
     await SpecialPowers.pushPrefEnv({
       set: [["browser.tabs.warnOnClose", true]],
     });
     info("Opening window...");
     const win = await BrowserTestUtils.openNewBrowserWindow();
     info("Opening Firefox View tab...");
     await openFirefoxViewTab(win);
     info("Trigger warnAboutClosingWindow()");
-    win.BrowserTryToCloseWindow();
+    win.BrowserCommands.tryToCloseWindow();
     await BrowserTestUtils.closeWindow(win);
     ok(!dialogObserver.wasOpened, "Dialog was not opened");
     dialogObserver.cleanup();
   }
 );
 
 add_task(
   async function on_close_warning_should_not_show_for_firefox_view_tab_non_macos() {

--- a/browser/components/sessionstore/test/browser_354894_perwindowpb.js
+++ b/browser/components/sessionstore/test/browser_354894_perwindowpb.js
@@ -16,17 +16,17 @@
  * attribute modified so that it's not considered a browser window any longer.
  * This is crucial, because otherwise there would be two browser windows around,
  * said main test window and the one opened by the tests, and hence the new
  * logic wouldn't be executed at all.
  * @note Mac only tests the new notifications, as restoring the last window is
  * not enabled on that platform (platform shim; the application is kept running
  * although there are no windows left)
  * @note There is a difference when closing a browser window with
- * BrowserTryToCloseWindow() as opposed to close(). The former will make
+ * BrowserCommands.tryToCloseWindow() as opposed to close(). The former will make
  * nsSessionStore restore a window next time it gets a chance and will post
  * notifications. The latter won't.
  */
 
 // The rejection "BrowserWindowTracker.getTopWindow(...) is null" is left
 // unhandled in some cases. This bug should be fixed, but for the moment this
 // file allows a class of rejections.
 //
@@ -177,30 +177,30 @@ let setupTest = async function (options,
 function injectTestTabs(win) {
   let promises = TEST_URLS.map(url =>
     BrowserTestUtils.addTab(win.gBrowser, url)
   ).map(tab => BrowserTestUtils.browserLoaded(tab.linkedBrowser));
   return Promise.all(promises);
 }
 
 /**
- * Attempts to close a window via BrowserTryToCloseWindow so that
+ * Attempts to close a window via BrowserCommands.tryToCloseWindow so that
  * we get the browser-lastwindow-close-requested and
  * browser-lastwindow-close-granted observer notifications.
  *
  * @param win (Window)
  *        The window to try to close
  * @returns Promise
  *        Resolves to true if the window closed, or false if the window
  *        was denied the ability to close.
  */
 function closeWindowForRestoration(win) {
   return new Promise(resolve => {
     let closePromise = BrowserTestUtils.windowClosed(win);
-    win.BrowserTryToCloseWindow();
+    win.BrowserCommands.tryToCloseWindow();
     if (!win.closed) {
       resolve(false);
       return;
     }
 
     closePromise.then(() => {
       resolve(true);
     });

--- a/browser/components/sessionstore/test/browser_580512.js
+++ b/browser/components/sessionstore/test/browser_580512.js
@@ -27,20 +27,20 @@ function test() {
   openWinWithCb(closeFirstWin, URIS_PINNED.concat(URIS_NORMAL_A));
 }
 
 function closeFirstWin(win) {
   win.gBrowser.pinTab(win.gBrowser.tabs[0]);
   win.gBrowser.pinTab(win.gBrowser.tabs[1]);
 
   let winClosed = BrowserTestUtils.windowClosed(win);
-  // We need to call BrowserTryToCloseWindow in order to trigger
+  // We need to call BrowserCommands.tryToCloseWindow in order to trigger
   // the machinery that chooses whether or not to save the session
   // for the last window.
-  win.BrowserTryToCloseWindow();
+  win.BrowserCommands.tryToCloseWindow();
   ok(win.closed, "window closed");
 
   winClosed.then(() => {
     openWinWithCb(
       checkSecondWin,
       URIS_NORMAL_B,
       URIS_PINNED.concat(URIS_NORMAL_B)
     );

--- a/browser/components/sessionstore/test/browser_589246.js
+++ b/browser/components/sessionstore/test/browser_589246.js
@@ -211,22 +211,22 @@ function onStateRestored() {
             "load",
             function () {
               if (shouldCloseTab == "one") {
                 newWin.gBrowser.removeTab(newTab2);
               } else if (shouldCloseTab == "both") {
                 newWin.gBrowser.removeTab(newTab);
                 newWin.gBrowser.removeTab(newTab2);
               }
-              newWin.BrowserTryToCloseWindow();
+              newWin.BrowserCommands.tryToCloseWindow();
             },
             { capture: true, once: true }
           );
         } else {
-          newWin.BrowserTryToCloseWindow();
+          newWin.BrowserCommands.tryToCloseWindow();
         }
       });
     },
     { once: true }
   );
 }
 
 // This will be called before the window is actually closed

--- a/devtools/client/framework/test/browser_toolbox_screenshot_tool.js
+++ b/devtools/client/framework/test/browser_toolbox_screenshot_tool.js
@@ -116,11 +116,11 @@ add_task(async function () {
 
   // Remove the downloaded screenshot file
   await IOUtils.remove(privateScreenshotFilePath);
 
   // cleanup the downloads
   await resetDownloads();
 
   const closePromise = BrowserTestUtils.windowClosed(privateWindow);
-  privateWindow.BrowserTryToCloseWindow();
+  privateWindow.BrowserCommands.tryToCloseWindow();
   await closePromise;
 });

--- a/devtools/client/webconsole/test/browser/browser_console_webconsole_private_browsing.js
+++ b/devtools/client/webconsole/test/browser/browser_console_webconsole_private_browsing.js
@@ -136,17 +136,17 @@ add_task(async function () {
   info("Wait for private log message");
   await onBrowserConsolePrivateLogMessage;
   info("Wait for private error message");
   await onBrowserConsolePrivateErrorMessage;
   ok(true, "Messages are displayed as expected");
 
   info("close the private window and check if private messages are removed");
   const onPrivateMessagesCleared = hud.ui.once("private-messages-cleared");
-  privateWindow.BrowserTryToCloseWindow();
+  privateWindow.BrowserCommands.tryToCloseWindow();
   await onPrivateMessagesCleared;
 
   ok(
     findConsoleAPIMessage(hud, NON_PRIVATE_MESSAGE),
     "non-private messages are still shown after private window closed"
   );
   assertNoPrivateMessages(hud);
 

--- a/devtools/shared/commands/resource/tests/browser_resources_last_private_context_exit.js
+++ b/devtools/shared/commands/resource/tests/browser_resources_last_private_context_exit.js
@@ -61,31 +61,31 @@ add_task(async function () {
   );
 
   info("Open a second private browsing window");
   const secondPrivateWindow = await BrowserTestUtils.openNewBrowserWindow({
     private: true,
   });
 
   info("Close the second private window");
-  secondPrivateWindow.BrowserTryToCloseWindow();
+  secondPrivateWindow.BrowserCommands.tryToCloseWindow();
 
   // Let a chance to an unexpected async event to be fired
   await wait(1000);
 
   is(
     availableResources.length,
     0,
     "We do not get any LAST_PRIVATE_CONTEXT_EXIT when closing the second private window only"
   );
 
   info(
     "close the private window and check if LAST_PRIVATE_CONTEXT_EXIT resource is sent"
   );
-  privateWindow.BrowserTryToCloseWindow();
+  privateWindow.BrowserCommands.tryToCloseWindow();
 
   info("Wait for LAST_PRIVATE_CONTEXT_EXIT");
   await waitFor(() => availableResources.length == 1);
   is(
     availableResources.length,
     1,
     "We get one LAST_PRIVATE_CONTEXT_EXIT when closing the last opened private window"
   );

--- a/devtools/startup/tests/browser/browser_shim_disable_devtools.js
+++ b/devtools/startup/tests/browser/browser_shim_disable_devtools.js
@@ -129,17 +129,17 @@ add_task(async function () {
   info("Close out the menu popups");
   await simulateMenuClosed(subMenu);
   await simulateMenuClosed(toolsMenuPopup);
 
   win.gBrowser.removeTab(tab);
 
   info("Close the test window");
   const winClosed = BrowserTestUtils.windowClosed(win);
-  win.BrowserTryToCloseWindow();
+  win.BrowserCommands.tryToCloseWindow();
   await winClosed;
 });
 
 function waitForDelayedStartupFinished(win) {
   return new Promise(resolve => {
     Services.obs.addObserver(function observer(subject) {
       if (win == subject) {
         Services.obs.removeObserver(

--- a/testing/talos/talos/tests/tart/addon/content/tart.js
+++ b/testing/talos/talos/tests/tart/addon/content/tart.js
@@ -141,17 +141,17 @@ Tart.prototype = {
     // --> many-tabs case which requires modified max-width will not go into v1. No need for now.
     // this._win.gBrowser.selectedTab.style.minWidth = "1px"; // Prevent overflow regrdless of DPI scale.
 
     return this._win.gBrowser.selectedTab;
   },
 
   clickCloseCurrentTab() {
     this._endDetection = this.tabDetector;
-    this._win.BrowserCloseTabOrWindow();
+    this._win.BrowserCommands.closeTabOrWindow();
     return this._win.gBrowser.selectedTab;
   },
 
   fadeOutCurrentTab() {
     this._endDetection = this.tabDetector;
     this._win.gBrowser.selectedTab.removeAttribute("fadein");
   },