gibberish qppeqrs zhen i type in firefox

So quickly checking the swapped keys, that looks like French [https://en.wikipedia.org/wiki/AZERTY AZERTY] layout instead of a QWERTY input method. Firefox most likely has no say in that as internationalization is handled on macOS level — however your macOS can be set to remember keyboard layout / input language per app, so if this doesn't affect the rest of your apps and only exhibits in Firefox, that pref might be targeted towards it. The best is to go into your System Settings › Keyboard › Input Sources and check "Show Input Sources In Menu Bar" which will give you a flag in the corner based on which app you're in — and also quick access to the dropdown there to change the per–app keyboard language.