I am using the direct download of Firefox and in V46 there is a bug (see their bugzilla #1234158) where using GTK3 3.20 it does not correctly show radio buttons or the scrollbars (scrollbars work but you cannot see the slider so you have to guess). I am reporting this here for the benefit of other susers who may use the direct download of Firefox. Not sure yet when the fix for this problem will be rolled out. There is also apparently a problem with the mouse cursor selection in FF.