When using Firefox on Android on a Xiaomi 15, it frequently freezes when coming back to the app and navigating. Generally the page will go blank white and the missing bar will appear but not move. If you go to the change app android screen (square button), then the thumbnail shows a transparent region where the page content should be. Closing the app from there and restarting it usually resolves it, but you will have to re-enter the address or search query.