Ui glitch or something
When I have either/both address bar or tabs set to the bottom of the browser, a white line appears at the bottom when fullscreening videos on sites such as youtube or vid.me.
Notice how this prevents the video from actually being fullscreen, resulting in black bars on both sides of the video.
I am using the Light theme, and have a 2560x1080 monitor.
EDIT: Found a thread from 7 months ago about the same issue. Spoiler alert: there isn't a solution there.