I just noticed this problem in Firefox today, after upgrading from Windows 8.1. I don't know for certain that it has anything to do with the upgrade however.
For a few websites, if I scroll the window down and then scroll back up, the text becomes degraded...fuzzy. Its almost like a double image.
Here is a screenshot of the original text:
And here is the fuzzy text:
And here is more weirdness. If I have less than a full screen in Firefox, even a small sliver of the desktop showing on one side, the fuzzy text never appears.
Testing on Chrome shows that it doesn't happen in that browser. Also, if I click something outside of Firefox, the text suddenly comes back into focus.
This happens at Endgadget, and in the forums at Videohelp.com, but nowhere else so far.
I've tried turning off hardware acceleration in Firefox, but no change.