Right now it's at the "release candidate" stage, meaning it's almost ready to be released as a stable version. They are 96% of the way to a final release: https://trac.torproject.org/projects/tor/milestone/Tor%3A%200.2.4.x-final This isn't like alpha software that we're talking about. The Tor Browser in TBB 2.4 is based on the same Firefox 17 that is bundled in TBB 2.3, so your safety (or danger) with regard to browser exploits is exactly the same.