Font size - One way for designing, another way for personal use?

[ytand]

I use Firefox 3, but the font size default is pretty tiny for me. But when I design sites, I want to test them in that browser with the default font size. Can anyone think of a way I can save my eyesight? I don't want to have to go to tools > options > content each time I get on to check my email and want to have larger text. And then I'd have to change it back when I was designing sites again.

For example, can I do something with profiles on my computer? (work vs. home) and have two different font sizes set? Or can I have two Firefoxes (same version) on my computer with different text sizes?

This is driving me nuts. I already am going to need glasses from all the squinting. Help!