It's getting annoying now. I tried it on IE (had to redownload the executable due to an "update"). Then IE blocks the add-on by default, and the website doesn't remind you that you have to allow it (as other websites usually do). I got the add-on to run, and now it's sitting at:
"Checking game data: 0% complete"
... and not moving out of there. I tried restarting the browser and the same thing still happens.
Yeah I know it's a beta but they already had a closed beta before. It doesn't look stable at all.
My Mario Kart Wii friend code: 2707-1866-0957