Kinda have the same issue on my new Motorola Edge 40 Neo running Android 13. As soon as im going to the homescreen right out of Firefox, the next time i try to go fullscreen with an already playing video, Firefox breaks.

Firefox->Play the Video->Fullscreen: works Firefox->Homescreenbutton->Firefox->Fullscreen->Play: works Firefox->Homescreenbutton->Firefox->Fullscreen->Play->normal mode->Play->Fullscreen: crashes to homescreen (always) Firefox->Homescreenbutton->Firefox->Play->Fullscreen: crashes to homescreen (always) Firefox->different app->Homescreenbutton->Firefox->Fullscreen->Play: works

I can still reopen Firefox after crashing but its no longer useable cause the browser is stuck in some kind of landscaped portrait mode. Everything is the size of lndscape mode, but its displayed in portrait mode, meaning i can only see the left third of the website. Restarting Firefox fixes this, till the next time I go homescreen out of Firefox.

I'm getting the same on a Pixel 7a. Firefox -> Play video -> Fullscreen: Works. Firefox -> Homescreen button -> Firefox -> Play video -> Fullscreen -> Firefox disappears.

Tested by playing videos from BBC News website. Also tested with Edge browers, but no issues observed when running same test.

This issue may also be recorded here: https://support.mozilla.org/en-US/questions/1426916