From 5e27368a4800775528bb8b4ed3b5954a5dc30764 Mon Sep 17 00:00:00 2001
From: "mr. m" <mr.m@tuta.com>
Date: Wed, 25 Feb 2026 20:31:28 +0100
Subject: [PATCH] fix: Fixed race conditions when syncing views through windows
 desktops, b=bug #12390, c=no-component

---
 src/zen/sessionstore/ZenWindowSync.sys.mjs | 25 ++++++++++++++--------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/src/zen/sessionstore/ZenWindowSync.sys.mjs b/src/zen/sessionstore/ZenWindowSync.sys.mjs
index 32200d625..361de92e0 100644
--- a/src/zen/sessionstore/ZenWindowSync.sys.mjs
+++ b/src/zen/sessionstore/ZenWindowSync.sys.mjs
@@ -1259,11 +1259,10 @@ class nsZenWindowSync {
     });
   }
 
-  async on_focus(aEvent) {
+  on_focus(aEvent) {
     if (typeof aEvent.target !== "object") {
       return;
     }
-    await this.#docShellSwitchPromise;
     const window = Services.focus.activeWindow;
     if (
       !window?.gBrowser ||
@@ -1273,23 +1272,31 @@ class nsZenWindowSync {
     ) {
       return;
     }
+    let promise = this.#docShellSwitchPromise;
     this.#lastFocusedWindow = new WeakRef(window);
     this.#lastSelectedTab = new WeakRef(window.gBrowser.selectedTab);
-    return (this.#docShellSwitchPromise = this.#onTabSwitchOrWindowFocus(window));
+    // eslint-disable-next-line no-async-promise-executor
+    this.#docShellSwitchPromise = new Promise(async (resolve) => {
+      await promise;
+      await this.#onTabSwitchOrWindowFocus(window);
+      resolve();
+    });
   }
 
-  async on_TabSelect(aEvent) {
-    await this.#docShellSwitchPromise;
+  on_TabSelect(aEvent) {
     const tab = aEvent.target;
     if (this.#lastSelectedTab?.deref() === tab) {
       return;
     }
     this.#lastSelectedTab = new WeakRef(tab);
     const previousTab = aEvent.detail.previousTab;
-    return (this.#docShellSwitchPromise = this.#onTabSwitchOrWindowFocus(
-      aEvent.target.ownerGlobal,
-      previousTab
-    ));
+    let promise = this.#docShellSwitchPromise;
+    // eslint-disable-next-line no-async-promise-executor
+    this.#docShellSwitchPromise = new Promise(async (resolve) => {
+      await promise;
+      await this.#onTabSwitchOrWindowFocus(tab.ownerGlobal, previousTab);
+      resolve();
+    });
   }
 
   on_SSWindowClosing(aEvent) {