The new version of Tor Browser Bundle (https://www.torproject.org/projects/torbrowser.html.en) doesn't have Vidalia (https://www.torproject.org/projects/vidalia.html.en) but only Firefox plugin "Torbutton". Before it was possible to click in Vidalia "New Identity" and proxy's IP address was changed. Problem is that similar ""New Identity" button in "Torrbutton" not only changes IP but also restarts browser.
How to change IP in Mac OS without restarting browser?
TorProject explains in FAQ:
Why does "New Identity" close all my open tabs? That's actually a feature, since it's discarding your application-level browser data too. But it sure is a surprising feature, for people who are used to Vidalia's "new identity" behavior.
We're working on ways to make the behavior less surprising, e.g. a popup warning or auto restoring tabs. See ticket #9906 and ticket 10400 to follow progress there.
In the mean time, you can get Vidalia's old "newnym" functionality by attaching a Vidalia to your TBB 3.x. See the instructions above. https://www.torproject.org/docs/faq.html.en#NewIdentityClosingTabs
But I don't see an option to download Vidalia for Mac OS any more. Perhaps it's possible to request for the new identity through the terminal?