So, i was hunting forever to allow IE users to change font size using their browser, and keep the site looking good in all browsers. Generally the easy way is to use a size of x-small for this. However, this does not work if that is not the size you want. So there is a 76% rule for body combine with a 1.0 em rule for tex tto help you control this… Very useful link example:
http://www.thenoodleincident.com/tutorials/typography/
enjoy