I've been encountering this problem since the last update. Basically there's a big bar on the bottom of the screen while watching videos on fullscreen on landscape mode as seen in the screenshot. My guess is it is the address bar's container since it is the only thing that can be placed at the bottom of the screen. On rare occurences, the notification shade (left side of the screen), navigation buttons (right side of the screen) leave bars after being hidden. So far these are the things that I've done to try and troubleshoot the issue: # Disabled all addons and tried them one-by-one # Disabled the hide address bar while scrollling in Firefox's settings # Show content on the notch on my phone's settings Though after disabling the hide address bar while scrolling, only the bar on the bottom is only showing (so far). I'm yet to see if the bars on the sides.