There's two types of Mafia Wars toolbar -- the official toolbar from Zynga, which makes it easy to monitor your game from the top of your browser, and the not-so-legal toolbar, aka Infinity MWToolbar, which helps you access your game faster, and, well, hack into it.
Even though players use the toolbar fairly regularly (in fact, the sixth version was just released), we don't necessarily condone using this bar -- it just might get you banned from your favorite Facebook game, and who wants that for for a few extra gifts?
The creators cross their hearts that this tool does not contain spyware, adware and that it will not collect any data "or even care about you." You decide whether you want to believe them or not. If you're aware of the risks (spam, phishing or Zynga banning you because you're hacking the game) and decide to download it anyway, you can find it at infinitymwtoolbar.com.