Anything to do with IE8 ? If using IE8 (or7) check in "page" on the toolbar that text size is set to largest. If IE8, I have the "zoom" at bottom right set to 112% custom to make text appear similar to using IE7. Messed up font's was one of my major moans with IE8.
With Firefox, go to the web page that is causing the problem. To enlarge the web page fonts, hold down the Control key and then rotate the mouse wheel to enlarge. If you do not have a mouse wheel, then hold down the Control key and then press down the "+" key. Repeatedly pressing the + key will continue to enlarge the fonts. The minus key reduces the font size.
Set to the size you require, close down the browser and open again. Visit the problem web page to see if the problem is resolved.