Had a browser crash at youtube, so bad that even after the crash the CPU was used 100%. Had to kill the process. Youtube was slow too, much worse than with opera.

Then there were problems with scrolling using the "down" key. It scrolled a bit but then scrolled back to its original position, very strange and not on all sites.

Those bugs made me uninstall the new browser. I was quite happy with opera and my own private tweaks (up/down key as page up/down, minimum fontsize etc). Probably this can be established on the firefox too, but I'm just not patient enough to be a beta-tester