Bug 1695639 - [remote] Enforce disabling of update checks. r=remote-protocol-reviewers,jdescottes

Use the preference "app.update.disabledForTesting" to enforce
that no update checks are performed when the Remote Agent is
active.

Differential Revision: https://phabricator.services.mozilla.com/D106909

remote/cdp/RecommendedPreferences.jsm

@@ -7,6 +7,13 @@
 var EXPORTED_SYMBOLS = ["RecommendedPreferences"];
 
 const RecommendedPreferences = new Map([
+  // Disable automatically upgrading Firefox
+  //
+  // Note: This preference should have already been set by the client when
+  // creating the profile. But if not and to absolutely make sure that updates
+  // of Firefox aren't downloaded and applied, enforce its presence.
+  ["app.update.disabledForTesting", true],
+
   // Allow the application to have focus even when it runs in the background.
   ["focusmanager.testmode", true],