yeah... that's really weird!!! v66.0.4 fixed that (there's a 66.0.5 on windows)!

You can try to fix it from about:support, but beware that it might delete some preferences, logins and other things like that...

by the way, you also have GNU IceCat Mobile -> Firefox minus proprietary things plus security measures ( https://www.gnu.org/software/gnuzilla/ )