I just installed it and was able to use it for about an hour before falling back to 3.x. Strangeness: periodically lose the ability to use the mouse wheel to scroll, scroll bar would jump to left side of browser, forms would no longer submit (and I get a message telling me that I am submitting a form across unencrypted sites; say 'continue' and it doesn't), 'options' dialog window blank except for 'ok' and 'cancel' buttons, add-ons I use on a daily basis not updated yet. I'll wait for 3.5.1 I guess.