Hmm there was a person having a similar problem last year[1]. Nobody else is
having this issue, so it appears to be a bug or you have accidentally
misconfigured something.
Can you try using Safe Mode? (see http://kb.mozillazine.org/Safe_Mode)
Also try following these instructions:
http://kb.mozillazine.org/Website_colors_are_wrong
http://kb.mozillazine.org/Websites_look_wrong
Most importantly, make sure "Page Style" in the View menu is not set to "No
Style".
If this doesn't work, you could try creating a new profile[2] and see if that
fixes your problem.
1: https://trisquel.info/en/forum/html5-abrowser#comment-23720
2: http://kb.mozillazine.org/Profile_Manager
