"Go to about:config and set browser.display.auto_quality_min_font_size to something improbably-high to turn it off.
I've had this problem with fonts I naively copied-and-pasted from other systems into Windows (eg, really old Mac fonts), and only on Firefox with this setting in effect."
"I surfed to github.com using FF 3.5.7 and didn't get this problem. (If you have an example of a problematic URL, please post.)
I would suggest uninstalling FF using revo, then reinstalling from scratch. Try then the display before installing any add-ons. Then install the add-ons in steps, checking the problem every step."
