I hope you skills are great, but that problem, and the fix it appears is ONLY for the Firefox Window, and the frame, URL bar, etc. is not changed. This is supposedly not a fix for the desktop? Many years ago, 5 or more, there was a FireFox problem what would black out the desktop, but that was fixed years ago? You could try a different version of FireFox too. I'm using the 64bit versions (Help -> About Firefox) but maybe the 32bit one would work better for you (or the 64bit depending on what you have?).
I would politely suggest that it is about time that Dell stepped up and started to take this problem seriously. Is there an official response from Dell on this?
XPS 8940, lock up issue Bios > 2.3.0