Ubuntu doesn't let you run Tor Browser by clicking on it

I just downloaded the Tor Browser Bundle for Linux. I'm running Ubuntu 13.04.

When I run "sh start.tor.browser" from the terminal, Vidalia launches just fine and says I'm connected to Tor, but no browser launches.

If I try just opening Firefox, check.torproject.org tells me I'm not running Tor. What's going wrong?

Trac:
Username: Caius