drops to the bottom of the screen

This is totally frustrating. If I am responding to a post or just entering text in a Facebook text window and I hit Backspace (which is my most used key), no matter where the text box is, it drops to the bottom of the screen and hides the text I am entering.

Does anybody know how to fix this?

I have a tenuous grip on reality as it is and this is driving me right over the edge.