As the title indicates, I noticed a sudden problem today in Firefox (on Windows XP) when checking Gmail – all of the text was bold. So I fired up Chrome to see if FF was the problem and all of the text in Chrome was in italics… These two problems together indicated a corrupted system font.
If you have ever have this problem, you need to reinstall the Arial font family (TrueType). The executable installer can be found here or here.