there is an uninstall script in c:program files (might be c:program files(x86) if you have a 64 bit PC). although Firefox can go tits up to the point it needs to be uninstalled, its unusual to have to do this. If it doesn’t work the “correct” way I’d remove the entire directory, install ccleaner and use that to get rid of any registry keys/remnants (beware that this will also remove all your active logins to sites) then reinstall firefox and immediately also install adblock edge, as its often ads and toolbars that hog resources and knacker browsers in this fashion.