These answers for the transition from the 2.4 Tor Browser Bundle to the 3.x series have been moved to the [https://www.torproject.org/docs/faq.html.en#tbb-3plus FAQ].
The 3.x series has a number of changes:
* They are built using [https://developer.mozilla.org/en-US/Firefox/Releases/24 Firefox version 24].
* [https://blog.torproject.org/blog/deterministic-builds-part-two-technical-details Reproducible builds] enable anyone to create a byte-for-byte identical copy of any bundle package.
* A Firefox extension called Tor Launcher replaces Vidalia.