If you need to have all your fonts on the page show up bigger (like me), you can download, install, and configure the Text Zoom extension. It blows up all of the text on a web page to whatever percentage you set it too (i.e. 135%).
To install: Start Firefox and goto /Tools/Options/Extenstions/ and click on Get New Extenstions. Search for the Text Zoom extension and download/install it.
Be sure to install it into your profile directory for each user (if it gives you a choice, can't remember if it does or not)