Have you tried Firefox's zoom feature? Font size and zoom - increase the size of web pages You can "zoom" all sites using this add-on: NoSquint. After setting your global zoom level, you can still fine-tune the zoom on individual sites. After installing NoSquint, click the % on the Add-on Bar to call up site preferences, then click the Global Settings button, then the Zooming tab.

If you don't have the Add-on Bar displayed, you can right-click the new tab button ("+") or a blank area of the tab bar to the right of it and choose Add-on Bar from the shortcut menu.

You can experiment with sizes larger than 125%, but I wouldn't go much higher than 150% unless you have a large high-resolution monitor.

If there are particular sites that still present a problem, feel free to post their URLs.

You can find more information about the zoom features Firefox offers in these articles:

Text zoom - For zooming text only

Page zoom - For zooming the whole page (including images etc.)

Thanks for the reply. Actually, I solved the problem by resetting Firefox to its default settings.