Odd internet text/font issue with my Vista PC.

Fig-D

So I was doing a little early spring cleaning today, not deleting any folders by hand mind you, using Add/Remove Programs and standard Disk Cleanup (in Properties on the hard drive, not a separate third party program). Somehow, in an effort to do things the right way, I managed to delete something that now effects my internet browsers. In FireFox, many sites display the wrong font, Google and Wikipedia being the two sites that I frequent the most that have this issue. This font, and I have no idea what it's called, isn't exactly easy to read. On Internet Explorer, which I try not to use, things are even worse. Text in some cases won't appear, and most of the time entire sites will fail to display.

What could I have done to cause such a problem and how can I restore things to the way they were? I know I can force a font in FireFox, but I'd rather not do that if I don't have to as the entire internet being displayed in only one font is rather boring.

EDIT: Guess I should mention that it doesn't do it the penny-arcade.com or the forums, if that means anything.