I am not too what exactly causes this (I suspect long periods of inactivity/not interacting with the browser) but when I switch back to one of my firefox windows on my laptop's monitor I get this black border/padding on the side/around my broswer. See attached images - (might be hard to spot, focus on the sides of the screen). First image is how the browser normally looks like. The 2nd image is with the random black border/padding. How do I stop this from happening? I've tried looking online for someone else havig the same issue but cannot seem to find anything.