[Bug]: Exiting from fullscreen IFrame removes widgets from navbar

[Thesola10]

Pre-Submission Checklist

• [X] I have checked the existing/closed issues to ensure this issue has not already been reported.
• [X] I am using the latest supported version of the browser.
• [X] I have tried disabling all browser extensions/add-ons to rule out interference from these.
• [X] I have tried clearing the browser cache and cookies.
• [X] I have checked with a new profile and the issue still occurs.
• [X] I have provided detailed step-by-step instructions on how to reproduce the issue.
• [x] I have included relevant screenshots or console outputs.
• [X] I have checked that this problem is not occurring in the latest version of Firefox ESR.
• [X] This issue is specific to this browser and does not occur in other browsers.

Bug Summary

When full-screening a video player or something else, if the full screen component was contained within an <iframe> instead of directly on the root page, exiting from full screen has the navbar missing most buttons.

Entering and existing the "Customize toolbar" menu restores navigation buttons.

This does not affect cases where the full screen widget is part of the root page, such as the official YouTube website.

Reproduction Steps

1. Navigate to a website where the video player is an <iframe>, e.g. this DuckDuckGo search embed
2. Click on the 'full screen' button or equivalent on the video player
3. Exit from full screen

Expected Behavior

The navigation toolbar looks the same as before full screen

Actual Behavior

The navigation toolbar is missing most buttons and widgets

Screenshots

Before:

After:

Browser Version

11.18.1

Operating System

Arch Linux (Flatpak)

Additional Context

Desktop: GNOME 46 (Wayland) with fractional scaling 125% UI: Lepton, auto-hide sidebar, hide sidebar header, show sidebar on top, bottom navbar GPU: Intel Iris Xe (i7-1265U) No userChrome.css