For some reason, a particular font has been replaced with another. So far it seems to be only affecting browsers. It started when I downloaded a font (which looks nothing like the one that is showing up everywhere). I have since uninstalled and removed this font but nothing has changed.

Has anyone had this problem before? How did you fix it? And what on earth causes it?

EDIT: In fact, it's only affecting Firefox... Not Safari. And my default font in FIrefox is set to Times.