There was an update a few weeks ago that seemed to mess with anti-aliasing in some applications. Firefox, Thunderbird, and the text in some apps such as Mousepad and Leafpad (but not the rest of the window) are affected, whereas Chrome and everything else seems to be just fine. Attached are two screenshots showing the difference between rendering in Firefox and Chrome.

The anti-aliasing settings are the same as they've always been, which have worked just fine - full hinting, RGB sub-pixel order.

I'm really not sure what's going on and am thinking that it might be faster to fix this problem by re-installing, but is there anything I can try first as re-installing is the last thing I want to do?

I'm running Xubuntu 12.04.