Text Zoom Instructions
Each modern browser has a built in text-zoom option for those users who may have impaired vision. The five main browsers are shown below with an image to describe the location of this menu option. On most browsers there is a keyboard and mouse shortcut to this option too.
Choosing the "Zoom Text Only" option will allow the page text to increase it's size without the entire site becoming bigger too. Experiment with and without this option enabled to see which works better for you.
Using Keyboard Only
Press ctrl and + to increase zoom levels, and ctrl and - to zoom out.
Using Keyboard and Mouse
Press the ctrl key and scroll using your mouse's scrollwheel. scrolling upward will increase the zoom, and scrolling down will zoom out.
Using Mouse Only
Text zoom menu location in Firefox 3:

Text zoom menu location in Internet Explorer 8

Text zoom menu location in Google Chrome

Text zoom menu location in Opera 9.6

Text zoom menu location in Safari 4
