This is a problem I've been having on and off for a while now. It seems to only happen on specific web sites, and only in Firefox (I use the Beta browser). On some sites the issue seems intermittent, while on others it's there every time. The issue is this: it seems that my keyboard (SwiftKey) fails to correctly recognize text input fields as such. Some times this leads to text input being doubled, as the autocorrect system fails to remove the direct input to replace it with the corrected word. Typically it means every word is capitalized, as every word is seen by the keyboard as the first word in a field. Some times the keyboard doesn't open at all. Erasing text is often either entirely impossible or extremely slow, as is navigating already input text.

Ive tried clearing both browser and keyboard caches with no change. Visiting the same sites in Chrome has everything work as intended.