The killer feature that Chrome has and Firefox is missing is quite simple: the ability to have “private” aka “anonymous” and non-private tabs open at the same time. As far as I can tell, with Firefox you can only be in one of these modes.

My vision of a next generation privacy browser would essentially allow you to have tabs in individual modes. With some simple rules for mode switching. Essentially, unknown sites should alwasy be opened in anonymous mode. Only sites that I register for should automatically switch to a tracked mode where cookies are kept, for my own convenience. And then there are sites in a safety category that should be isolated from any other contents such as my banking site. Going to these sites should require me to manually switch modes (except when using my bookmark). Embedding, framing and such things to these sites should be impossible.

On a side note, having TOR tabs would also be nice.