I recently heard about a service called BrowserStack that I just had to try out. We’ve seen services before that let you view a screenshot of what your site looks like in other browsers, but nothing comes close to what this has to offer. You literally get hands-on time with your site in Firefox, IE, Chrome, Safari, and Opera with a wide array of versions supported.
I should note that BrowserStack is not really free, but when you signup you get 60-minutes of usage to figure out if it’s worth paying for. The reason you’d want to use something like this is that you’re essentially connecting to a virtual machine where you can interact with the browser and take advantage of the bundled web developer debugging tools, such as Firebug.
If you use up the 60-minute of time you’ll need to spring for one of the paid plans, which start at $19/month for one user to get unlimited access. If you’re a full-time web developer that is quite a deal given the amount of frustration it can cause trying to test sites in the 20 different browsers/versions BrowserStack offers.