I found this in a few different places around the 'net - hopefully it's helpful:
Change Web Page Font Size on the Fly
If your mouse contains a wheel for scrolling, you can change font size on the fly when viewing a Web page.
- Press and hold Ctrl.
- Scroll down (or towards yourself) to enlarge the font size.
- Scroll up (or away from yourself) to reduce the font size.
You might find it useful to reduce font size when printing a Web page, so that you can fit more content on the page.