Adding upstream version 124.0.1.upstream/124.0.1

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

10 files changed, 1325 insertions, 0 deletions

diff --git a/toolkit/mozapps/handling/ContentDispatchChooser.sys.mjs b/toolkit/mozapps/handling/ContentDispatchChooser.sys.mjs
new file mode 100644
index 0000000000..e916fdad4c
--- /dev/null
+++ b/toolkit/mozapps/handling/ContentDispatchChooser.sys.mjs
@@ -0,0 +1,465 @@
+/* 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/. */
+
+// Constants
+
+import { XPCOMUtils } from "resource://gre/modules/XPCOMUtils.sys.mjs";
+
+import { E10SUtils } from "resource://gre/modules/E10SUtils.sys.mjs";
+
+const DIALOG_URL_APP_CHOOSER =
+  "chrome://mozapps/content/handling/appChooser.xhtml";
+const DIALOG_URL_PERMISSION =
+  "chrome://mozapps/content/handling/permissionDialog.xhtml";
+
+const gPrefs = {};
+XPCOMUtils.defineLazyPreferenceGetter(
+  gPrefs,
+  "promptForExternal",
+  "network.protocol-handler.prompt-from-external",
+  true
+);
+
+const PROTOCOL_HANDLER_OPEN_PERM_KEY = "open-protocol-handler";
+const PERMISSION_KEY_DELIMITER = "^";
+
+export class nsContentDispatchChooser {
+  /**
+   * Prompt the user to open an external application.
+   * If the triggering principal doesn't have permission to open apps for the
+   * protocol of aURI, we show a permission prompt first.
+   * If the caller has permission and a preferred handler is set, we skip the
+   * dialogs and directly open the handler.
+   * @param {nsIHandlerInfo} aHandler - Info about protocol and handlers.
+   * @param {nsIURI} aURI - URI to be handled.
+   * @param {nsIPrincipal} [aPrincipal] - Principal which triggered the load.
+   * @param {BrowsingContext} [aBrowsingContext] - Context of the load.
+   * @param {bool} [aTriggeredExternally] - Whether the load came from outside
+   * this application.
+   */
+  async handleURI(
+    aHandler,
+    aURI,
+    aPrincipal,
+    aBrowsingContext,
+    aTriggeredExternally = false
+  ) {
+    let callerHasPermission = this._hasProtocolHandlerPermission(
+      aHandler.type,
+      aPrincipal,
+      aTriggeredExternally
+    );
+
+    // Force showing the dialog for links passed from outside the application.
+    // This avoids infinite loops, see bug 1678255, bug 1667468, etc.
+    if (
+      aTriggeredExternally &&
+      gPrefs.promptForExternal &&
+      // ... unless we intend to open the link with a website or extension:
+      !(
+        aHandler.preferredAction == Ci.nsIHandlerInfo.useHelperApp &&
+        aHandler.preferredApplicationHandler instanceof Ci.nsIWebHandlerApp
+      )
+    ) {
+      aHandler.alwaysAskBeforeHandling = true;
+    }
+
+    if ("mailto" === aURI.scheme) {
+      Glean.protocolhandlerMailto.visit.record({
+        triggered_externally: aTriggeredExternally,
+      });
+    }
+
+    // Skip the dialog if a preferred application is set and the caller has
+    // permission.
+    if (
+      callerHasPermission &&
+      !aHandler.alwaysAskBeforeHandling &&
+      (aHandler.preferredAction == Ci.nsIHandlerInfo.useHelperApp ||
+        aHandler.preferredAction == Ci.nsIHandlerInfo.useSystemDefault)
+    ) {
+      try {
+        aHandler.launchWithURI(aURI, aBrowsingContext);
+        return;
+      } catch (error) {
+        // We are not supposed to ask, but when file not found the user most likely
+        // uninstalled the application which handles the uri so we will continue
+        // by application chooser dialog.
+        if (error.result == Cr.NS_ERROR_FILE_NOT_FOUND) {
+          aHandler.alwaysAskBeforeHandling = true;
+        } else {
+          throw error;
+        }
+      }
+    }
+
+    let shouldOpenHandler = false;
+
+    try {
+      shouldOpenHandler = await this._prompt(
+        aHandler,
+        aPrincipal,
+        callerHasPermission,
+        aBrowsingContext,
+        aURI
+      );
+    } catch (error) {
+      console.error(error.message);
+    }
+
+    if (!shouldOpenHandler) {
+      return;
+    }
+
+    // Site was granted permission and user chose to open application.
+    // Launch the external handler.
+    aHandler.launchWithURI(aURI, aBrowsingContext);
+  }
+
+  /**
+   * Get the name of the application set to handle the the protocol.
+   * @param {nsIHandlerInfo} aHandler - Info about protocol and handlers.
+   * @returns {string|null} - Human readable handler name or null if the user
+   * is expected to set a handler.
+   */
+  _getHandlerName(aHandler) {
+    if (aHandler.alwaysAskBeforeHandling) {
+      return null;
+    }
+    if (
+      aHandler.preferredAction == Ci.nsIHandlerInfo.useSystemDefault &&
+      aHandler.hasDefaultHandler
+    ) {
+      return aHandler.defaultDescription;
+    }
+    return aHandler.preferredApplicationHandler?.name;
+  }
+
+  /**
+   * Show permission or/and app chooser prompt.
+   * @param {nsIHandlerInfo} aHandler - Info about protocol and handlers.
+   * @param {nsIPrincipal} aPrincipal - Principal which triggered the load.
+   * @param {boolean} aHasPermission - Whether the caller has permission to
+   * open the protocol.
+   * @param {BrowsingContext} [aBrowsingContext] - Context associated with the
+   * protocol navigation.
+   */
+  async _prompt(aHandler, aPrincipal, aHasPermission, aBrowsingContext, aURI) {
+    let shouldOpenHandler = false;
+    let resetHandlerChoice = false;
+    let updateHandlerData = false;
+
+    const isStandardProtocol = E10SUtils.STANDARD_SAFE_PROTOCOLS.includes(
+      aURI.scheme
+    );
+    const {
+      hasDefaultHandler,
+      preferredApplicationHandler,
+      alwaysAskBeforeHandling,
+    } = aHandler;
+
+    // This will skip the app chooser dialog flow unless the user explicitly opts to choose
+    // another app in the permission dialog.
+    if (
+      !isStandardProtocol &&
+      hasDefaultHandler &&
+      preferredApplicationHandler == null &&
+      alwaysAskBeforeHandling
+    ) {
+      aHandler.alwaysAskBeforeHandling = false;
+      updateHandlerData = true;
+    }
+
+    // If caller does not have permission, prompt the user.
+    if (!aHasPermission) {
+      let canPersistPermission = this._isSupportedPrincipal(aPrincipal);
+
+      let outArgs = Cc["@mozilla.org/hash-property-bag;1"].createInstance(
+        Ci.nsIWritablePropertyBag
+      );
+      // Whether the permission request was granted
+      outArgs.setProperty("granted", false);
+      // If the user wants to select a new application for the protocol.
+      // This will cause us to show the chooser dialog, even if an app is set.
+      outArgs.setProperty("resetHandlerChoice", null);
+      // If the we should store the permission and not prompt again for it.
+      outArgs.setProperty("remember", null);
+
+      await this._openDialog(
+        DIALOG_URL_PERMISSION,
+        {
+          handler: aHandler,
+          principal: aPrincipal,
+          browsingContext: aBrowsingContext,
+          outArgs,
+          canPersistPermission,
+          preferredHandlerName: this._getHandlerName(aHandler),
+        },
+        aBrowsingContext
+      );
+      if (!outArgs.getProperty("granted")) {
+        // User denied request
+        return false;
+      }
+
+      // Check if user wants to set a new application to handle the protocol.
+      resetHandlerChoice = outArgs.getProperty("resetHandlerChoice");
+
+      // If the user wants to select a new app we don't persist the permission.
+      if (!resetHandlerChoice && aPrincipal) {
+        let remember = outArgs.getProperty("remember");
+        this._updatePermission(aPrincipal, aHandler.type, remember);
+      }
+
+      shouldOpenHandler = true;
+    }
+
+    // Prompt if the user needs to make a handler choice for the protocol.
+    if (aHandler.alwaysAskBeforeHandling || resetHandlerChoice) {
+      // User has not set a preferred application to handle this protocol scheme.
+      // Open the application chooser dialog
+      let outArgs = Cc["@mozilla.org/hash-property-bag;1"].createInstance(
+        Ci.nsIWritablePropertyBag
+      );
+      outArgs.setProperty("openHandler", false);
+      outArgs.setProperty("preferredAction", aHandler.preferredAction);
+      outArgs.setProperty(
+        "preferredApplicationHandler",
+        aHandler.preferredApplicationHandler
+      );
+      outArgs.setProperty(
+        "alwaysAskBeforeHandling",
+        aHandler.alwaysAskBeforeHandling
+      );
+      let usePrivateBrowsing = aBrowsingContext?.usePrivateBrowsing;
+      await this._openDialog(
+        DIALOG_URL_APP_CHOOSER,
+        {
+          handler: aHandler,
+          outArgs,
+          usePrivateBrowsing,
+          enableButtonDelay: aHasPermission,
+        },
+        aBrowsingContext
+      );
+
+      shouldOpenHandler = outArgs.getProperty("openHandler");
+
+      // If the user accepted the dialog, apply their selection.
+      if (shouldOpenHandler) {
+        for (let prop of [
+          "preferredAction",
+          "preferredApplicationHandler",
+          "alwaysAskBeforeHandling",
+        ]) {
+          aHandler[prop] = outArgs.getProperty(prop);
+        }
+        updateHandlerData = true;
+      }
+    }
+
+    if (updateHandlerData) {
+      // Store handler data
+      Cc["@mozilla.org/uriloader/handler-service;1"]
+        .getService(Ci.nsIHandlerService)
+        .store(aHandler);
+    }
+
+    return shouldOpenHandler;
+  }
+
+  /**
+   * Test if a given principal has the open-protocol-handler permission for a
+   * specific protocol.
+   * @param {string} scheme - Scheme of the protocol.
+   * @param {nsIPrincipal} aPrincipal - Principal to test for permission.
+   * @returns {boolean} - true if permission is set, false otherwise.
+   */
+  _hasProtocolHandlerPermission(scheme, aPrincipal, aTriggeredExternally) {
+    // Permission disabled by pref
+    if (!nsContentDispatchChooser.isPermissionEnabled) {
+      return true;
+    }
+
+    // If a handler is set to open externally by default we skip the dialog.
+    if (
+      Services.prefs.getBoolPref(
+        "network.protocol-handler.external." + scheme,
+        false
+      )
+    ) {
+      return true;
+    }
+
+    if (
+      !aPrincipal ||
+      (aPrincipal.isSystemPrincipal && !aTriggeredExternally)
+    ) {
+      return false;
+    }
+
+    let key = this._getSkipProtoDialogPermissionKey(scheme);
+    return (
+      Services.perms.testPermissionFromPrincipal(aPrincipal, key) ===
+      Services.perms.ALLOW_ACTION
+    );
+  }
+
+  /**
+   * Get open-protocol-handler permission key for a protocol.
+   * @param {string} aProtocolScheme - Scheme of the protocol.
+   * @returns {string} - Permission key.
+   */
+  _getSkipProtoDialogPermissionKey(aProtocolScheme) {
+    return (
+      PROTOCOL_HANDLER_OPEN_PERM_KEY +
+      PERMISSION_KEY_DELIMITER +
+      aProtocolScheme
+    );
+  }
+
+  /**
+   * Opens a dialog as a SubDialog on tab level.
+   * If we don't have a BrowsingContext or tab level dialogs are not supported,
+   * we will fallback to a standalone window.
+   * @param {string} aDialogURL - URL of the dialog to open.
+   * @param {Object} aDialogArgs - Arguments passed to the dialog.
+   * @param {BrowsingContext} [aBrowsingContext] - BrowsingContext associated
+   * with the tab the dialog is associated with.
+   */
+  async _openDialog(aDialogURL, aDialogArgs, aBrowsingContext) {
+    // Make the app chooser dialog resizable
+    let resizable = `resizable=${
+      aDialogURL == DIALOG_URL_APP_CHOOSER ? "yes" : "no"
+    }`;
+
+    if (aBrowsingContext) {
+      let window = aBrowsingContext.topChromeWindow;
+      if (!window) {
+        throw new Error(
+          "Can't show external protocol dialog. BrowsingContext has no chrome window associated."
+        );
+      }
+
+      let { topFrameElement } = aBrowsingContext;
+      if (topFrameElement?.tagName != "browser") {
+        throw new Error(
+          "Can't show external protocol dialog. BrowsingContext has no browser associated."
+        );
+      }
+
+      // If the app does not support window.gBrowser or getTabDialogBox(),
+      // fallback to the standalone application chooser window.
+      let getTabDialogBox = window.gBrowser?.getTabDialogBox;
+      if (getTabDialogBox) {
+        return getTabDialogBox(topFrameElement).open(
+          aDialogURL,
+          {
+            features: resizable,
+            allowDuplicateDialogs: false,
+            keepOpenSameOriginNav: true,
+          },
+          aDialogArgs
+        ).closedPromise;
+      }
+    }
+
+    // If we don't have a BrowsingContext, we need to show a standalone window.
+    let win = Services.ww.openWindow(
+      null,
+      aDialogURL,
+      null,
+      `chrome,dialog=yes,centerscreen,${resizable}`,
+      aDialogArgs
+    );
+
+    // Wait until window is closed.
+    return new Promise(resolve => {
+      win.addEventListener("unload", function onUnload(event) {
+        if (event.target.location != aDialogURL) {
+          return;
+        }
+        win.removeEventListener("unload", onUnload);
+        resolve();
+      });
+    });
+  }
+
+  /**
+   * Update the open-protocol-handler permission for the site which triggered
+   * the dialog. Sites with this permission may skip this dialog.
+   * @param {nsIPrincipal} aPrincipal - subject to update the permission for.
+   * @param {string} aScheme - Scheme of protocol to allow.
+   * @param {boolean} aAllow - Whether to set / unset the permission.
+   */
+  _updatePermission(aPrincipal, aScheme, aAllow) {
+    // If enabled, store open-protocol-handler permission for content principals.
+    if (
+      !nsContentDispatchChooser.isPermissionEnabled ||
+      aPrincipal.isSystemPrincipal ||
+      !this._isSupportedPrincipal(aPrincipal)
+    ) {
+      return;
+    }
+
+    let principal = aPrincipal;
+
+    // If this action was triggered by an extension content script then set the
+    // permission on the extension's principal.
+    let addonPolicy = aPrincipal.contentScriptAddonPolicy;
+    if (addonPolicy) {
+      principal = Services.scriptSecurityManager.principalWithOA(
+        addonPolicy.extension.principal,
+        principal.originAttributes
+      );
+    }
+
+    let permKey = this._getSkipProtoDialogPermissionKey(aScheme);
+    if (aAllow) {
+      Services.perms.addFromPrincipal(
+        principal,
+        permKey,
+        Services.perms.ALLOW_ACTION,
+        Services.perms.EXPIRE_NEVER
+      );
+    } else {
+      Services.perms.removeFromPrincipal(principal, permKey);
+    }
+  }
+
+  /**
+   * Determine if we can use a principal to store permissions.
+   * @param {nsIPrincipal} aPrincipal - Principal to test.
+   * @returns {boolean} - true if we can store permissions, false otherwise.
+   */
+  _isSupportedPrincipal(aPrincipal) {
+    if (!aPrincipal) {
+      return false;
+    }
+
+    // If this is an add-on content script then we will be able to store
+    // permissions against the add-on's principal.
+    if (aPrincipal.contentScriptAddonPolicy) {
+      return true;
+    }
+
+    return ["http", "https", "moz-extension", "file"].some(scheme =>
+      aPrincipal.schemeIs(scheme)
+    );
+  }
+}
+
+nsContentDispatchChooser.prototype.classID = Components.ID(
+  "e35d5067-95bc-4029-8432-e8f1e431148d"
+);
+nsContentDispatchChooser.prototype.QueryInterface = ChromeUtils.generateQI([
+  "nsIContentDispatchChooser",
+]);
+
+XPCOMUtils.defineLazyPreferenceGetter(
+  nsContentDispatchChooser,
+  "isPermissionEnabled",
+  "security.external_protocol_requires_permission",
+  true
+);
diff --git a/toolkit/mozapps/handling/components.conf b/toolkit/mozapps/handling/components.conf
new file mode 100644
index 0000000000..95afe50a87
--- /dev/null
+++ b/toolkit/mozapps/handling/components.conf
@@ -0,0 +1,14 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+Classes = [
+    {
+        'cid': '{e35d5067-95bc-4029-8432-e8f1e431148d}',
+        'contract_ids': ['@mozilla.org/content-dispatch-chooser;1'],
+        'esModule': 'resource://gre/modules/ContentDispatchChooser.sys.mjs',
+        'constructor': 'nsContentDispatchChooser',
+    },
+]
diff --git a/toolkit/mozapps/handling/content/appChooser.js b/toolkit/mozapps/handling/content/appChooser.js
new file mode 100644
index 0000000000..2958ad68b4
--- /dev/null
+++ b/toolkit/mozapps/handling/content/appChooser.js
@@ -0,0 +1,369 @@
+/* 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/. */
+
+const { PrivateBrowsingUtils } = ChromeUtils.importESModule(
+  "resource://gre/modules/PrivateBrowsingUtils.sys.mjs"
+);
+const { EnableDelayHelper } = ChromeUtils.importESModule(
+  "resource://gre/modules/PromptUtils.sys.mjs"
+);
+
+class MozHandler extends window.MozElements.MozRichlistitem {
+  static get markup() {
+    return `
+    <vbox pack="center">
+      <html:img alt="" height="32" width="32" loading="lazy" />
+    </vbox>
+    <vbox flex="1">
+      <label class="name"/>
+      <label class="description"/>
+    </vbox>
+    `;
+  }
+
+  connectedCallback() {
+    this.textContent = "";
+    this.appendChild(this.constructor.fragment);
+    this.initializeAttributeInheritance();
+  }
+
+  static get inheritedAttributes() {
+    return {
+      img: "src=image,disabled",
+      ".name": "value=name,disabled",
+      ".description": "value=description,disabled",
+    };
+  }
+
+  get label() {
+    return `${this.getAttribute("name")} ${this.getAttribute("description")}`;
+  }
+}
+
+customElements.define("mozapps-handler", MozHandler, {
+  extends: "richlistitem",
+});
+
+window.addEventListener("DOMContentLoaded", () => dialog.initialize(), {
+  once: true,
+});
+
+let dialog = {
+  /**
+   * This function initializes the content of the dialog.
+   */
+  initialize() {
+    let args = window.arguments[0].wrappedJSObject || window.arguments[0];
+    let { handler, outArgs, usePrivateBrowsing, enableButtonDelay } = args;
+
+    this._handlerInfo = handler.QueryInterface(Ci.nsIHandlerInfo);
+    this._outArgs = outArgs;
+
+    this.isPrivate =
+      usePrivateBrowsing ||
+      (window.opener && PrivateBrowsingUtils.isWindowPrivate(window.opener));
+
+    this._dialog = document.querySelector("dialog");
+    this._itemChoose = document.getElementById("item-choose");
+    this._rememberCheck = document.getElementById("remember");
+
+    // Register event listener for the checkbox hint.
+    this._rememberCheck.addEventListener("change", () => this.onCheck());
+
+    document.addEventListener("dialogaccept", () => {
+      this.onAccept();
+    });
+
+    // UI is ready, lets populate our list
+    this.populateList();
+
+    this.initL10n();
+
+    if (enableButtonDelay) {
+      this._delayHelper = new EnableDelayHelper({
+        disableDialog: () => {
+          this._acceptBtnDisabled = true;
+          this.updateAcceptButton();
+        },
+        enableDialog: () => {
+          this._acceptBtnDisabled = false;
+          this.updateAcceptButton();
+        },
+        focusTarget: window,
+      });
+    }
+  },
+
+  initL10n() {
+    let rememberLabel = document.getElementById("remember-label");
+    document.l10n.setAttributes(rememberLabel, "chooser-dialog-remember", {
+      scheme: this._handlerInfo.type,
+    });
+
+    let description = document.getElementById("description");
+    document.l10n.setAttributes(description, "chooser-dialog-description", {
+      scheme: this._handlerInfo.type,
+    });
+  },
+
+  /**
+   * Populates the list that a user can choose from.
+   */
+  populateList: function populateList() {
+    var items = document.getElementById("items");
+    var possibleHandlers = this._handlerInfo.possibleApplicationHandlers;
+    var preferredHandler = this._handlerInfo.preferredApplicationHandler;
+    for (let i = possibleHandlers.length - 1; i >= 0; --i) {
+      let app = possibleHandlers.queryElementAt(i, Ci.nsIHandlerApp);
+      let elm = document.createXULElement("richlistitem", {
+        is: "mozapps-handler",
+      });
+      elm.setAttribute("name", app.name);
+      elm.obj = app;
+
+      // We defer loading the favicon so it doesn't delay load. The dialog is
+      // opened in a SubDialog which will only show on window load.
+      if (app instanceof Ci.nsILocalHandlerApp) {
+        // See if we have an nsILocalHandlerApp and set the icon
+        let uri = Services.io.newFileURI(app.executable);
+        elm.setAttribute("image", "moz-icon://" + uri.spec + "?size=32");
+      } else if (app instanceof Ci.nsIWebHandlerApp) {
+        let uri = Services.io.newURI(app.uriTemplate);
+        if (/^https?$/.test(uri.scheme)) {
+          // Unfortunately we can't use the favicon service to get the favicon,
+          // because the service looks for a record with the exact URL we give
+          // it, and users won't have such records for URLs they don't visit,
+          // and users won't visit the handler's URL template, they'll only
+          // visit URLs derived from that template (i.e. with %s in the template
+          // replaced by the URL of the content being handled).
+          elm.setAttribute("image", uri.prePath + "/favicon.ico");
+        }
+        elm.setAttribute("description", uri.prePath);
+
+        // Check for extensions needing private browsing access before
+        // creating UI elements.
+        if (this.isPrivate) {
+          let policy = WebExtensionPolicy.getByURI(uri);
+          if (policy && !policy.privateBrowsingAllowed) {
+            elm.setAttribute("disabled", true);
+            this.getPrivateBrowsingDisabledLabel().then(label => {
+              elm.setAttribute("description", label);
+            });
+            if (app == preferredHandler) {
+              preferredHandler = null;
+            }
+          }
+        }
+      } else if (app instanceof Ci.nsIDBusHandlerApp) {
+        elm.setAttribute("description", app.method);
+      } else if (!(app instanceof Ci.nsIGIOMimeApp)) {
+        // We support GIO application handler, but no action required there
+        throw new Error("unknown handler type");
+      }
+
+      items.insertBefore(elm, this._itemChoose);
+      if (preferredHandler && app == preferredHandler) {
+        this.selectedItem = elm;
+      }
+    }
+
+    if (this._handlerInfo.hasDefaultHandler) {
+      let elm = document.createXULElement("richlistitem", {
+        is: "mozapps-handler",
+      });
+      elm.id = "os-default-handler";
+      elm.setAttribute("name", this._handlerInfo.defaultDescription);
+
+      items.insertBefore(elm, items.firstChild);
+      if (
+        this._handlerInfo.preferredAction == Ci.nsIHandlerInfo.useSystemDefault
+      ) {
+        this.selectedItem = elm;
+      }
+    }
+
+    // Add gio handlers
+    if (Cc["@mozilla.org/gio-service;1"]) {
+      let gIOSvc = Cc["@mozilla.org/gio-service;1"].getService(
+        Ci.nsIGIOService
+      );
+      var gioApps = gIOSvc.getAppsForURIScheme(this._handlerInfo.type);
+      for (let handler of gioApps.enumerate(Ci.nsIHandlerApp)) {
+        // OS handler share the same name, it's most likely the same app, skipping...
+        if (handler.name == this._handlerInfo.defaultDescription) {
+          continue;
+        }
+        // Check if the handler is already in possibleHandlers
+        let appAlreadyInHandlers = false;
+        for (let i = possibleHandlers.length - 1; i >= 0; --i) {
+          let app = possibleHandlers.queryElementAt(i, Ci.nsIHandlerApp);
+          // nsGIOMimeApp::Equals is able to compare with nsILocalHandlerApp
+          if (handler.equals(app)) {
+            appAlreadyInHandlers = true;
+            break;
+          }
+        }
+        if (!appAlreadyInHandlers) {
+          let elm = document.createXULElement("richlistitem", {
+            is: "mozapps-handler",
+          });
+          elm.setAttribute("name", handler.name);
+          elm.obj = handler;
+          items.insertBefore(elm, this._itemChoose);
+        }
+      }
+    }
+
+    items.ensureSelectedElementIsVisible();
+  },
+
+  /**
+   * Brings up a filepicker and allows a user to choose an application.
+   */
+  async chooseApplication() {
+    let title = await this.getChooseAppWindowTitle();
+
+    var fp = Cc["@mozilla.org/filepicker;1"].createInstance(Ci.nsIFilePicker);
+    fp.init(window, title, Ci.nsIFilePicker.modeOpen);
+    fp.appendFilters(Ci.nsIFilePicker.filterApps);
+
+    fp.open(rv => {
+      if (rv == Ci.nsIFilePicker.returnOK && fp.file) {
+        let uri = Services.io.newFileURI(fp.file);
+
+        let handlerApp = Cc[
+          "@mozilla.org/uriloader/local-handler-app;1"
+        ].createInstance(Ci.nsILocalHandlerApp);
+        handlerApp.executable = fp.file;
+
+        // if this application is already in the list, select it and don't add it again
+        let parent = document.getElementById("items");
+        for (let i = 0; i < parent.childNodes.length; ++i) {
+          let elm = parent.childNodes[i];
+          if (
+            elm.obj instanceof Ci.nsILocalHandlerApp &&
+            elm.obj.equals(handlerApp)
+          ) {
+            parent.selectedItem = elm;
+            parent.ensureSelectedElementIsVisible();
+            return;
+          }
+        }
+
+        let elm = document.createXULElement("richlistitem", {
+          is: "mozapps-handler",
+        });
+        elm.setAttribute("name", fp.file.leafName);
+        elm.setAttribute("image", "moz-icon://" + uri.spec + "?size=32");
+        elm.obj = handlerApp;
+
+        parent.selectedItem = parent.insertBefore(elm, parent.firstChild);
+        parent.ensureSelectedElementIsVisible();
+      }
+    });
+  },
+
+  /**
+   * Function called when the OK button is pressed.
+   */
+  onAccept() {
+    this.updateHandlerData(this._rememberCheck.checked);
+    this._outArgs.setProperty("openHandler", true);
+  },
+
+  /**
+   * Determines if the accept button should be disabled or not
+   */
+  updateAcceptButton() {
+    this._dialog.setAttribute(
+      "buttondisabledaccept",
+      this._acceptBtnDisabled || this._itemChoose.selected
+    );
+  },
+
+  /**
+   * Update the handler info to reflect the user choice.
+   * @param {boolean} skipAsk - Whether we should persist the application
+   * choice and skip asking next time.
+   */
+  updateHandlerData(skipAsk) {
+    // We need to make sure that the default is properly set now
+    if (this.selectedItem.obj) {
+      // default OS handler doesn't have this property
+      this._outArgs.setProperty(
+        "preferredAction",
+        Ci.nsIHandlerInfo.useHelperApp
+      );
+      this._outArgs.setProperty(
+        "preferredApplicationHandler",
+        this.selectedItem.obj
+      );
+    } else {
+      this._outArgs.setProperty(
+        "preferredAction",
+        Ci.nsIHandlerInfo.useSystemDefault
+      );
+    }
+    this._outArgs.setProperty("alwaysAskBeforeHandling", !skipAsk);
+  },
+
+  /**
+   * Updates the UI based on the checkbox being checked or not.
+   */
+  onCheck() {
+    if (document.getElementById("remember").checked) {
+      document.getElementById("remember-text").setAttribute("visible", "true");
+    } else {
+      document.getElementById("remember-text").removeAttribute("visible");
+    }
+  },
+
+  /**
+   * Function called when the user double clicks on an item of the list
+   */
+  onDblClick: function onDblClick() {
+    if (this.selectedItem == this._itemChoose) {
+      this.chooseApplication();
+    } else {
+      this._dialog.acceptDialog();
+    }
+  },
+
+  // Getters / Setters
+
+  /**
+   * Returns/sets the selected element in the richlistbox
+   */
+  get selectedItem() {
+    return document.getElementById("items").selectedItem;
+  },
+  set selectedItem(aItem) {
+    document.getElementById("items").selectedItem = aItem;
+  },
+
+  /**
+   *  Lazy l10n getter for the title of the app chooser window
+   */
+  async getChooseAppWindowTitle() {
+    if (!this._chooseAppWindowTitle) {
+      this._chooseAppWindowTitle = await document.l10n.formatValues([
+        "choose-other-app-window-title",
+      ]);
+    }
+    return this._chooseAppWindowTitle;
+  },
+
+  /**
+   * Lazy l10n getter for handler menu items which are disabled due to private
+   * browsing.
+   */
+  async getPrivateBrowsingDisabledLabel() {
+    if (!this._privateBrowsingDisabledLabel) {
+      this._privateBrowsingDisabledLabel = await document.l10n.formatValues([
+        "choose-dialog-privatebrowsing-disabled",
+      ]);
+    }
+    return this._privateBrowsingDisabledLabel;
+  },
+};
diff --git a/toolkit/mozapps/handling/content/appChooser.xhtml b/toolkit/mozapps/handling/content/appChooser.xhtml
new file mode 100644
index 0000000000..8ac984e387
--- /dev/null
+++ b/toolkit/mozapps/handling/content/appChooser.xhtml
@@ -0,0 +1,73 @@
+<?xml version="1.0"?>
+<!-- This Source Code Form is subject to the terms of the Mozilla Public
+   - License, v. 2.0. If a copy of the MPL was not distributed with this
+   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
+
+<!DOCTYPE window>
+
+<window
+  persist="width height screenX screenY"
+  aria-describedby="description-text"
+  xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
+  xmlns:html="http://www.w3.org/1999/xhtml"
+  data-l10n-id="chooser-window"
+  data-l10n-attrs="style"
+>
+  <dialog
+    id="handling"
+    buttons="accept,cancel"
+    defaultButton="none"
+    data-l10n-id="chooser-dialog"
+    data-l10n-attrs="buttonlabelaccept, buttonaccesskeyaccept"
+  >
+    <linkset>
+      <html:link rel="stylesheet" href="chrome://global/skin/global.css" />
+      <html:link
+        rel="stylesheet"
+        href="chrome://mozapps/content/handling/handler.css"
+      />
+      <html:link
+        rel="stylesheet"
+        href="chrome://mozapps/skin/handling/handling.css"
+      />
+
+      <html:link rel="localization" href="branding/brand.ftl" />
+      <html:link rel="localization" href="toolkit/global/handlerDialog.ftl" />
+    </linkset>
+
+    <script
+      src="chrome://mozapps/content/handling/appChooser.js"
+      type="application/javascript"
+    />
+
+    <description id="description" />
+
+    <vbox id="chooser" flex="1">
+      <richlistbox
+        id="items"
+        flex="1"
+        ondblclick="dialog.onDblClick();"
+        onselect="dialog.updateAcceptButton();"
+      >
+        <richlistitem id="item-choose" orient="horizontal" selected="true">
+          <label data-l10n-id="choose-other-app-description" flex="1" />
+          <button
+            oncommand="dialog.chooseApplication();"
+            data-l10n-id="choose-app-btn"
+          />
+        </richlistitem>
+      </richlistbox>
+    </vbox>
+
+    <vbox id="rememberContainer">
+      <html:label class="toggle-container-with-text">
+        <html:input type="checkbox" id="remember" />
+        <html:span id="remember-label" />
+      </html:label>
+      <description
+        id="remember-text"
+        data-l10n-id="chooser-dialog-remember-extra"
+      />
+    </vbox>
+  </dialog>
+</window>
diff --git a/toolkit/mozapps/handling/content/handler.css b/toolkit/mozapps/handling/content/handler.css
new file mode 100644
index 0000000000..2e60b1b41f
--- /dev/null
+++ b/toolkit/mozapps/handling/content/handler.css
@@ -0,0 +1,59 @@
+/* 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/. */
+
+@namespace html "http://www.w3.org/1999/xhtml";
+
+#description {
+  font-weight: bold;
+}
+
+#remember-text:not([visible]) {
+  visibility: hidden;
+}
+
+dialog {
+  padding: 16px calc(16px - 4px);
+}
+
+#items,
+label, description {
+  margin: 0;
+}
+
+#items label {
+  margin-inline: 4px;
+}
+
+#description,
+#description-box,
+#rememberContainer,
+#chooser {
+  margin: 0 4px 16px;
+}
+
+#chooser img:is(:-moz-broken, :not([src])) {
+  visibility: hidden;
+}
+
+/* avoid double inline margins when #description is nested: */
+#description-box > #description {
+  margin-inline: 0;
+}
+
+/* Parent selector to win on specificity against common.css */
+#rememberContainer > .toggle-container-with-text {
+  align-items: baseline;
+  color: var(--text-color-deemphasized);
+}
+
+.toggle-container-with-text > html|input[type="checkbox"] {
+  margin-inline-end: 8px;
+  /* Ensure the checkbox is properly aligned with the text: */
+  translate: 0 calc(1px + max(60% - .6em, 0px));
+}
+
+#rememberContainer:not([hidden]) {
+  /* Ensure we don't get sized to the smallest child when the checkbox text wraps. */
+  display: block;
+}
diff --git a/toolkit/mozapps/handling/content/permissionDialog.js b/toolkit/mozapps/handling/content/permissionDialog.js
new file mode 100644
index 0000000000..de9df6c3ac
--- /dev/null
+++ b/toolkit/mozapps/handling/content/permissionDialog.js
@@ -0,0 +1,223 @@
+/* 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/. */
+
+const { EnableDelayHelper } = ChromeUtils.importESModule(
+  "resource://gre/modules/PromptUtils.sys.mjs"
+);
+
+let dialog = {
+  /**
+   * This function initializes the content of the dialog.
+   */
+  initialize() {
+    let args = window.arguments[0].wrappedJSObject || window.arguments[0];
+    let {
+      handler,
+      principal,
+      outArgs,
+      canPersistPermission,
+      preferredHandlerName,
+      browsingContext,
+    } = args;
+
+    this._handlerInfo = handler.QueryInterface(Ci.nsIHandlerInfo);
+    this._principal = principal?.QueryInterface(Ci.nsIPrincipal);
+    this._addonPolicy =
+      this._principal?.addonPolicy ?? this._principal?.contentScriptAddonPolicy;
+    this._browsingContext = browsingContext;
+    this._outArgs = outArgs.QueryInterface(Ci.nsIWritablePropertyBag);
+    this._preferredHandlerName = preferredHandlerName;
+
+    this._dialog = document.querySelector("dialog");
+    this._checkRemember = document.getElementById("remember");
+    this._checkRememberContainer = document.getElementById("rememberContainer");
+
+    if (!canPersistPermission) {
+      this._checkRememberContainer.hidden = true;
+    }
+
+    let changeAppLink = document.getElementById("change-app");
+
+    // allow the user to choose another application if they wish,
+    // but don't offer this if the protocol was opened via
+    // system principal (URLbar) and there's a preferred handler
+    if (this._preferredHandlerName && !this._principal?.isSystemPrincipal) {
+      changeAppLink.hidden = false;
+
+      changeAppLink.addEventListener("click", () => this.onChangeApp());
+    }
+    document.addEventListener("dialogaccept", () => this.onAccept());
+    this.initL10n();
+
+    this._delayHelper = new EnableDelayHelper({
+      disableDialog: () => {
+        this._dialog.setAttribute("buttondisabledaccept", true);
+      },
+      enableDialog: () => {
+        this._dialog.setAttribute("buttondisabledaccept", false);
+      },
+      focusTarget: window,
+    });
+  },
+
+  /**
+   * Checks whether the principal that triggered this dialog is top level
+   * (not embedded in a frame).
+   * @returns {boolean} - true if principal is top level, false otherwise.
+   * If the triggering principal is null this method always returns false.
+   */
+  triggeringPrincipalIsTop() {
+    if (!this._principal) {
+      return false;
+    }
+
+    let topContentPrincipal =
+      this._browsingContext?.top.embedderElement?.contentPrincipal;
+    if (!topContentPrincipal) {
+      return false;
+    }
+    return this._principal.equals(topContentPrincipal);
+  },
+
+  /**
+   * Determines the l10n ID to use for the dialog description, depending on
+   * the triggering principal and the preferred application handler.
+   */
+  get l10nDescriptionId() {
+    if (this._addonPolicy) {
+      if (this._preferredHandlerName) {
+        return "permission-dialog-description-extension-app";
+      }
+      return "permission-dialog-description-extension";
+    }
+
+    if (this._principal?.schemeIs("file")) {
+      if (this._preferredHandlerName) {
+        return "permission-dialog-description-file-app";
+      }
+      return "permission-dialog-description-file";
+    }
+
+    if (this._principal?.isSystemPrincipal && this._preferredHandlerName) {
+      return "permission-dialog-description-system-app";
+    }
+
+    if (this._principal?.isSystemPrincipal && !this._preferredHandlerName) {
+      return "permission-dialog-description-system-noapp";
+    }
+
+    // We only show the website address if the request didn't come from the top
+    // level frame. If we can't get a host to display, fall back to the copy
+    // without host.
+    if (!this.triggeringPrincipalIsTop() && this.displayPrePath) {
+      if (this._preferredHandlerName) {
+        return "permission-dialog-description-host-app";
+      }
+      return "permission-dialog-description-host";
+    }
+
+    if (this._preferredHandlerName) {
+      return "permission-dialog-description-app";
+    }
+
+    return "permission-dialog-description";
+  },
+
+  /**
+   * Determines the l10n ID to use for the "remember permission" checkbox,
+   * depending on the triggering principal and the preferred application
+   * handler.
+   */
+  get l10nCheckboxId() {
+    if (!this._principal) {
+      return null;
+    }
+
+    if (this._addonPolicy) {
+      return "permission-dialog-remember-extension";
+    }
+    if (this._principal.schemeIs("file")) {
+      return "permission-dialog-remember-file";
+    }
+    return "permission-dialog-remember";
+  },
+
+  /**
+   * Computes the prePath to show in the prompt. It's the prePath of the site
+   * that wants to navigate to the external protocol.
+   * @returns {string|null} - prePath to show, or null if we can't derive an
+   * exposable prePath from the triggering principal.
+   */
+  get displayPrePath() {
+    if (!this._principal) {
+      return null;
+    }
+
+    // NullPrincipals don't expose a meaningful prePath. Instead use the
+    // precursorPrincipal, which the NullPrincipal was derived from.
+    if (this._principal.isNullPrincipal) {
+      return this._principal.precursorPrincipal?.exposablePrePath;
+    }
+
+    return this._principal?.exposablePrePath;
+  },
+
+  initL10n() {
+    // The UI labels depend on whether we will show the application chooser next
+    // or directly open the assigned protocol handler.
+
+    // Fluent id for dialog accept button
+    let idAcceptButton;
+    let acceptButton = this._dialog.getButton("accept");
+
+    if (this._preferredHandlerName) {
+      idAcceptButton = "permission-dialog-btn-open-link";
+    } else {
+      idAcceptButton = "permission-dialog-btn-choose-app";
+
+      let descriptionExtra = document.getElementById("description-extra");
+      descriptionExtra.hidden = false;
+      acceptButton.addEventListener("click", () => this.onChangeApp());
+    }
+    document.l10n.setAttributes(acceptButton, idAcceptButton);
+
+    let description = document.getElementById("description");
+
+    let host = this.displayPrePath;
+    let scheme = this._handlerInfo.type;
+
+    document.l10n.setAttributes(description, this.l10nDescriptionId, {
+      host,
+      scheme,
+      extension: this._addonPolicy?.name,
+      appName: this._preferredHandlerName,
+    });
+
+    if (!this._checkRememberContainer.hidden) {
+      let checkboxLabel = document.getElementById("remember-label");
+      document.l10n.setAttributes(checkboxLabel, this.l10nCheckboxId, {
+        host,
+        scheme,
+      });
+    }
+  },
+
+  onAccept() {
+    this._outArgs.setProperty("remember", this._checkRemember.checked);
+    this._outArgs.setProperty("granted", true);
+  },
+
+  onChangeApp() {
+    this._outArgs.setProperty("resetHandlerChoice", true);
+
+    // We can't call the dialogs accept handler here. If the accept button is
+    // still disabled, it will prevent closing.
+    this.onAccept();
+    window.close();
+  },
+};
+
+window.addEventListener("DOMContentLoaded", () => dialog.initialize(), {
+  once: true,
+});
diff --git a/toolkit/mozapps/handling/content/permissionDialog.xhtml b/toolkit/mozapps/handling/content/permissionDialog.xhtml
new file mode 100644
index 0000000000..bdc67d9e68
--- /dev/null
+++ b/toolkit/mozapps/handling/content/permissionDialog.xhtml
@@ -0,0 +1,56 @@
+<?xml version="1.0"?>
+<!-- This Source Code Form is subject to the terms of the Mozilla Public
+   - License, v. 2.0. If a copy of the MPL was not distributed with this
+   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
+
+<!DOCTYPE window>
+
+<window
+  aria-describedby="description"
+  xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
+  xmlns:html="http://www.w3.org/1999/xhtml"
+>
+  <dialog
+    buttons="accept,cancel"
+    defaultButton="none"
+    data-l10n-attrs="buttonlabelaccept, buttonaccesskeyaccept"
+  >
+    <linkset>
+      <html:link rel="stylesheet" href="chrome://global/skin/global.css" />
+      <html:link
+        rel="stylesheet"
+        href="chrome://mozapps/content/handling/handler.css"
+      />
+
+      <html:link rel="localization" href="toolkit/global/handlerDialog.ftl" />
+    </linkset>
+
+    <script
+      src="chrome://mozapps/content/handling/permissionDialog.js"
+      type="application/javascript"
+    />
+
+    <vbox id="description-box">
+      <description id="description"></description>
+      <label
+        id="change-app"
+        hidden="true"
+        is="text-link"
+        data-l10n-id="permission-dialog-set-change-app-link"
+      ></label>
+      <description
+        id="description-extra"
+        hidden="true"
+        data-l10n-id="permission-dialog-unset-description"
+      >
+      </description>
+    </vbox>
+
+    <vbox id="rememberContainer">
+      <html:label class="toggle-container-with-text">
+        <html:input type="checkbox" id="remember" />
+        <html:span id="remember-label" />
+      </html:label>
+    </vbox>
+  </dialog>
+</window>
diff --git a/toolkit/mozapps/handling/jar.mn b/toolkit/mozapps/handling/jar.mn
new file mode 100644
index 0000000000..769c757ed7
--- /dev/null
+++ b/toolkit/mozapps/handling/jar.mn
@@ -0,0 +1,11 @@
+# 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/.
+
+toolkit.jar:
+% content mozapps %content/mozapps/
+  content/mozapps/handling/handler.css               (content/handler.css)
+  content/mozapps/handling/appChooser.xhtml          (content/appChooser.xhtml)
+  content/mozapps/handling/appChooser.js             (content/appChooser.js)
+  content/mozapps/handling/permissionDialog.xhtml    (content/permissionDialog.xhtml)
+  content/mozapps/handling/permissionDialog.js       (content/permissionDialog.js)
diff --git a/toolkit/mozapps/handling/metrics.yaml b/toolkit/mozapps/handling/metrics.yaml
new file mode 100644
index 0000000000..2466f0993c
--- /dev/null
+++ b/toolkit/mozapps/handling/metrics.yaml
@@ -0,0 +1,37 @@
+
+# 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/.
+
+# Adding a new metric? We have docs for that!
+
+# https://firefox-source-docs.mozilla.org/toolkit/components/glean/user/new_definitions_file.html
+
+---
+$schema: moz://mozilla.org/schemas/glean/metrics/2-0-0
+$tags:
+  - 'Firefox :: General'
+
+protocolhandler.mailto:
+  visit:
+    type: event
+    description: >
+      a URI of type mailto was visited. Furthermore we want to know if from
+      within the browser.
+    bugs:
+      - https://bugzilla.mozilla.org/1864216
+    data_reviews:
+      - https://bugzilla.mozilla.org/show_bug.cgi?id=1864216#c8
+    notification_emails:
+      - install-update@mozilla.com
+    expires: never
+    extra_keys:
+      triggered_externally:
+        description: >
+          If Firefox was invoked to handle the link this value is true and if
+          the callee comes from within Firefox, this value is false
+        type: boolean
+    send_in_pings:
+      - active
+      - events
+      - metrics
diff --git a/toolkit/mozapps/handling/moz.build b/toolkit/mozapps/handling/moz.build
new file mode 100644
index 0000000000..0fd8fe7d35
--- /dev/null
+++ b/toolkit/mozapps/handling/moz.build
@@ -0,0 +1,18 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+with Files("**"):
+    BUG_COMPONENT = ("Firefox", "File Handling")
+
+EXTRA_JS_MODULES += [
+    "ContentDispatchChooser.sys.mjs",
+]
+
+XPCOM_MANIFESTS += [
+    "components.conf",
+]
+
+JAR_MANIFESTS += ["jar.mn"]