Hi arronvdc, I understand when watching youtube in Firefox in fullscreen that there difference in resolution and screen size than that of the monitor.

Sometimes yotube files are limited to the quality that they are uploaded as.

However the screen that is active when you fullscreen the browser will take that meta data I believe. However its smaller than both of them which is strange. If you move the widow to the desired monitor, then hit full screen is there a difference?

Yes there is a difference. Btw im using a laptop (My laptops screens is 1366 x 786 ) And my 2nd screen is 1280x720. Here is a screenshot of my 2th screen.

I found this little hack that you might find useful: https://www.youtube.com/watch?v=GNQdVCqFNdE

Thats not my problem (I dont upload videos) I watch videos and see the black bars.