If you've been on Grooveshark's Beta page lately you'll know they released an all-HTML version of their massive jukebox. However it only works in Chrome, or so they say.
Goto: http://preview.grooveshark.com/ and sign in. It will soon complain about not being able to load in your browser.
In the address bar copy and paste:
Then press enter. All the warnings should disappear.
Have fun playing :)