Like any CSS Sushi Chef worth his Shio, you should be using a Reset CSS style sheet to bring all your browsers into line before you carve out your tasty styles.
However sometimes when debugging someone elses work which might not have a Reset CSS stylesheet, you might find yourself taking a few stabs in Firebug to see what could be the cause of their CSS woes.
This can be slow guess work looking through the DOM Tree finding the culprits, or you might be trying to find the problem in another browser such as IE-vil.
This little bookmarklet will inject the Yahoo Reset CSS into the page your on. Making any further guesses or adjustments you make less likely to be related to some default margin issues.
Drag this link into your bookmarks -> Yahoo Reset CSS Bookmarklet