I watch a lot of sports on my large desktop monitor, mostly via "Watch ESPN using ESPN3, ESPN+, SEC, and ACC. Within the last few days going to full screen mode leaves me with narrow black bars on both sides and the bottom, with none at the top. This happens on my desktop and twp laptops that I use. This is happening in Firefox but Microsoft Edge is still showing these same videos with absolutely no borders, like Firefox used to do. I love Firefox but will be using Edge to watch my sports until this is resolved. I "sync" Firefox with all three computers so may some inadvertent setting is affecting them all. Strangely, this doesn't seem to be affecting You Tube