I like Chrome's "private browsing" mode better than Firefox's though. Mostly because I can have private and non-private windows open at the same time (and they're properly sandboxed from each other).

./firefox -P someotherprofile -no-remote

(assuming you created someotherprofile via Profile Manager - it's dead easy)

(Works on Windows, too)

Right, but in Chrome it's as easy as Ctrl + Shift + n from another Chrome window.

edit: I'll note that I don't believe that the parent to this post should be down-voted. It was informative and on-topic.

Maybe I would have deserved a downvote for forgetting to mention that after opening the second Firefox session you still have to switch it to Private Browsing :-))))