Been experiencing this issue for a few weeks now. Running 15.1 and Facebook just freezes when you click a comment and have the Apple Keyboard attached. Tried the Accessibility-Keyboard-Full Keyboard Access trick and switched access on which solved it but added annoying shortcuts and blue boxes around everything.
Trick here is to go into Accessibility-Keyboard-Full Keyboard Access-Commands and turn absolutely all options to Clear, except the arrow keys as they’re still quite useful to use on the keyboard. Lastly, go back into Full Keyboard Access and under Appearance, click Hide and select 1s.
Works like it used to again and no blue boxes.