Bug 1696160 - [remote] Only reset those recommended preferences that were previously set. r=remote-protocol-reviewers,jdescottes

Differential Revision: https://phabricator.services.mozilla.com/D107054

remote/cdp/RecommendedPreferences.jsm

@@ -6,23 +6,25 @@
 
 var EXPORTED_SYMBOLS = ["RecommendedPreferences"];
 
-const RecommendedPreferences = {
+const RecommendedPreferences = new Map([
   // Allow the application to have focus even when it runs in the background.
-  "focusmanager.testmode": true,
+  ["focusmanager.testmode", true],
 
   // Avoid breaking odd-runs of firefox because of it running in safe mode.
   // Firefox will run in safe mode alsmost on every even/odd runs as
   // Puppeteer may very easily shutdown Firefox process brutaly and force
   // it to run in safe mode in the next run.
-  "toolkit.startup.max_resumed_crashes": -1,
+  ["toolkit.startup.max_resumed_crashes", -1],
 
   // Prevent various error message on the console
   // jest-puppeteer asserts that no error message is emitted by the console
-  "browser.contentblocking.features.standard":
+  [
+    "browser.contentblocking.features.standard",
     "-tp,tpPrivate,cookieBehavior0,-cm,-fp",
-  "network.cookie.cookieBehavior": 0,
+  ],
+  ["network.cookie.cookieBehavior", 0],
 
   // Only allow the old modal dialogs. This should be removed when there is
   // support for the new modal UI (see Bug 1686743).
-  "prompts.contentPromptSubDialog": false,
-};
+  ["prompts.contentPromptSubDialog", false],
+]);

remote/components/RemoteAgent.jsm

@@ -29,6 +29,10 @@ const FORCE_LOCAL = "remote.force-local";
 const LOOPBACKS = ["localhost", "127.0.0.1", "[::1]"];
 
 class RemoteAgentClass {
+  constructor() {
+    this.alteredPrefs = new Set();
+  }
+
   get listening() {
     return !!this.server && !this.server.isStopped();
   }
@@ -76,7 +80,13 @@ class RemoteAgentClass {
       port = -1;
     }
 
-    Preferences.set(RecommendedPreferences);
+    for (let [k, v] of RecommendedPreferences) {
+      if (!Preferences.isSet(k)) {
+        log.debug(`Setting recommended pref ${k} to ${v}`);
+        Preferences.set(k, v);
+        this.alteredPrefs.add(k);
+      }
+    }
 
     this.server = new HttpServer();
     this.server.registerPrefixHandler("/json/", new JSONHandler(this));
@@ -114,10 +124,11 @@ class RemoteAgentClass {
 
   close() {
     try {
-      // if called early at startup, preferences may not be available
-      try {
-        Preferences.reset(Object.keys(RecommendedPreferences));
-      } catch (e) {}
+      for (let k of this.alteredPrefs) {
+        log.debug(`Resetting recommended pref ${k}`);
+        Preferences.reset(k);
+      }
+      this.alteredPrefs.clear();
 
       // destroy targets before stopping server,
       // otherwise the HTTP will fail to stop