I can't even really explain this one so I had to record a video. 

 

I have no idea what is going on and it only seems to happen in Firefox with me but I'm hoping you've seen something similar and have an easy fix. If it's not an easy fix, then I imagine it would be extremely difficult and not worth the time. Basically, all of the drop down lists in my editor start repeating themselves all the way down the screen and the 'Visible Borders' and one other icon keep flashing. 

 

* Note : I am not touching the computer at all while this is going on.