How will my site render on all browsers?

I recently was browsing the Mozilla Tools listing, and I cam across another amazing tool created by Adobe called BrowserLab. Browserlab allows you to view any publicly viewable webpage as it would be seen by Firefox (OSX & XP v. 2,3,3.5) Chrome (XP v. 3), IE (XP v. 6,7,8) and Safari (OSX v. 3,4). You can overlay each browser view to see differences, as well as use a rule to measure positioning of elements on page. Check it out! BrowserLab (You have to create an Adobe account, which takes 10 seconds...just do it)