1px black line in Firefox full screen mode

Question

In Firefox, there is a 1PX black line on top of the screen in full-screen mode.

Is there any way to remove it with website CSS code?

Answer 1

Add the following snippet to your userChrome.css file to make the 1px black line completely transparent (and thereby invisible) while preserving the default functionality of displaying the tab bar when you mouse-over the top 1px of the screen:

#fullscr-toggler { background-color: rgba(0, 0, 0, 0) !important; }

Alternatively, if you don't want the tab bar to be revealed when you mouse-over the top 1px of the screen, then use this snippet instead of the one shown above:

#fullscr-toggler { display: none; }

See this old (locked) MozillaZine forum thread for more information.