You said in your original post that you did a system restore that didn't work. Are you sure you restored to a date that you are sure you didn't have that problem? Are you sure that after the restore, after the computer restarted, did it say "The system restored successfully" and NOT "The system failed to restore to that date"? Look to see if you have restore points as far back as a few months and try restoring to them. If this doesn't work, I will try to think of something else.
Make sure your Firefox is up-to-date = v3.6.8
Try uninstalling the new fonts you installed, restart and try again. (It's anyways not good to install too many fonts. Only install ones you need and not just full packages of thousands of fonts).
Try to go to "Tools" and then to "Options...". When there, go to "Content". Under "Fonts & Colors" click on "Advanced". Uncheck the box that reads "Allow pages to choose their own fonts...".
Be careful with the following tip!
Open Firefox and type in URL: about:config
You will get a warning. Click OK (But I'd advise to leave the option to warn you again in the future CHECKED)
In the Filter, type font.
My settings for a few are:
browser.display.auto_quality_min_font_size = 20
browser.display.use_document_fonts = 1
font.default.el = serif
font.minimum-size.el = 0
font.minimum-size.th = 10
font.size.fixed.el = 13
font.size.variable.el = 16
See if these are like yours.
DO NOT CHANGE ANYTHING ELSE ON THIS PAGE!!!!
Download freeware Ultimate Windows Tweaker Link Removed - Invalid URL and go to Internet Explorer Tab and click "Restore Defaults" and Apply.