tor-browser

commit 9605c52d304b53d294a45085ba5c6cc4a84bb261
parent bfad0646716e74e8a39b40cf9ed4f1fb890da400
Author: Jens Stutte <jstutte@mozilla.com>
Date:   Thu,  2 Oct 2025 13:40:18 +0000

Bug 1991846 - _RFPHelper._handleLetterboxingPrefChanged should avoid to register the observer twice.  r=tjr

There might be a way to solve this at test level by pushing only the prefs that really need to be changed, but it feels safer to solve it here.

Differential Revision: https://phabricator.services.mozilla.com/D267224

Diffstat:
M
toolkit/components/resistfingerprinting/RFPHelper.sys.mjs
 | 
15
+++++++++++++--

1 file changed, 13 insertions(+), 2 deletions(-)
diff --git a/toolkit/components/resistfingerprinting/RFPHelper.sys.mjs b/toolkit/components/resistfingerprinting/RFPHelper.sys.mjs
@@ -35,6 +35,11 @@ function log(...args) {
 class _RFPHelper {
   _resizeObservers = new WeakMap();
 
+  // Track the observer status. It looks like pref changes can be notified
+  // also if the pref is actually unchanged. This might be a tests-only issue
+  // where we repeatedly push the prefs. See bug 1992137.
+  _letterboxingPrefObserversAdded = false;
+
   // ============================================================================
   // Shared Setup
   // ============================================================================
@@ -289,11 +294,17 @@ class _RFPHelper {
 
   _handleLetterboxingPrefChanged() {
     if (Services.prefs.getBoolPref(kPrefLetterboxing, false)) {
-      Services.ww.registerNotification(this);
+      if (!this._letterboxingPrefObserversAdded) {
+        Services.ww.registerNotification(this);
+        this._letterboxingPrefObserversAdded = true;
+      }
       this._attachAllWindows();
     } else {
       this._detachAllWindows();
-      Services.ww.unregisterNotification(this);
+      if (this._letterboxingPrefObserversAdded) {
+        Services.ww.unregisterNotification(this);
+        this._letterboxingPrefObserversAdded = false;
+      }
     }
   }