Great,that's very good tool having all useful features as'Browser Launcher' to opens the current page in the chosen browser,Testing Toolbar to emulate various screen resolutions and many more
but one thing hurt me that it is underconstruction that mean we cannot trust its results right now...... can we ?:?:
Well hopefully the results will slowly get better :)
I haven't tried it but the idea sounds awesome and would be very very useful. Especially being able to see what your site looks like in previous versions of browsers.