Mysteriously increased line-height for text in browsers

When I view web pages for which the text formatting has not been explicitly set through CSS styles, the line-height of the text is about twice what it should be by default. This problem is evident in both Safari and FireFox (though it does not appear to effect Opera).

This problem only occurs in my user account. Other accounts on the same machine work as expected. I've tried deleting the font caches (with Font Explorer X), but that doesn't appear to have had any effect.

Is there a particular preference file, or something along those lines, that may have gotten corrupted to cause this behavior? Perhaps something I can delete to return things back to their defaults?