I posted downthread - I tried this fix, but all it seems to be doing is resetting the text to 100% while still keeping the interface impossibly large, which is the opposite of what I want.
Updated today and have this issue too. Windows text size 125% now makes Firefox interface take up too much space - and the text is still too small! And 125% was actually my compromize that made the text just barely big enough, while not at the same...