Cannot reproduce this issue with the same version of Firefox on an android 15 tablet.
I’m going to try to reproduce this in an android 9 emulator with a phone-styled viewport. The performance was terrible for some reason, probably my tablet’s 4gb of ram, but i will try again
I tried android 9 with virtual master now, here are the results:
Basically what the author said, but on my emulator window, the white does not go all the way to the top.