Pinned extension icons order gets reversed after opening Customize Toolbar

[troybao]

Preliminary Checks

• I have read and understood the important section above.
• I have searched existing issues and avoided creating duplicates.
• I am not filing an enhancement request.
• I have checked that this issue cannot be reproduced on Mozilla Firefox.
• I have checked that this issue can be reproduced once I removed all my Mods and Custom CSS.

What happened?

When extension icons are pinned to the toolbar, opening the "Customize Toolbar" panel causes the order of the pinned extension icons to reverse (e.g. an order of 1234 becomes 4321). This happens even if no changes are made and no save action is taken — simply opening the Customize Toolbar panel and pressing Esc to exit is enough to trigger it. The only way to restore the correct order is to fully close and reopen the browser.

This bug only occurs when the Browser Layout is set to "Only Sidebar". I tested other layouts with a top toolbar and the pinned icon order remains correct there.

Expected behavior

Opening and closing the Customize Toolbar panel without saving should not alter the order of pinned extension icons.

Actual behavior

The order of pinned extension icons is reversed every time the Customize Toolbar panel is opened, when using the "Only Sidebar" layout.

Steps to reproduce

1. Set Browser Layout to "Only Sidebar"
2. Pin several extension icons to the toolbar in a specific order
3. Open Customize Toolbar
4. Press Esc to close the panel without making any changes or saving
5. Observe that the pinned extension icons are now in reverse order
6. Restart the browser — the pinned icon order returns to normal.

Screenshots and videos

Video_2026-07-27_145925.mp4

Version

1.21.9b

What platform are you seeing the problem on?

Windows - x64

What component is this issue related to?

Customizable UI / Toolbars

Relevant log output if applicable