Fill Screen Anywhere — Zoom Into Videos от Farid Zelli

Zoom into videos across numerous streaming platforms.

Mobile usage:
Pinch in and out on your screen, or long press the full screen button (YouTube only) to toggle zoom.

Desktop usage:
Open any full screen video and look for the "Fill Screen" button on the right side.
The default keyboard shortcut is Ctrl+Alt+F.
See Manage extension shortcuts in Firefox for more info.

Note:
On hardened browsers, enable the "Allow for all sites" permission after installation.

This lightweight add-on is fully open-source.