A co-worker of mine, Luke Larsen, posted a great article on our company blog about a cool app called Multi Fire Fox. Here is an excerpt:

As a front end guy I am always looking for ways to help our website look the same in all browsers. When FireFox 3 came out I was all excited for a new browser, however this also means that I would have yet another browser to test in until FireFox 2 phases out. I have noticed some small differences in how FF2 and FF3 render.

Head over to The Code Dojo to check it out. It is a great tool.