Nightly
Working from latest Moz nightly on Linux...consider me impressed.
I'm espically fond of the new cookie managment features. I still like the way the Konqueror basically allows you to create a cookie rule set on the fly if you set the "prompt" option for setting cookies. Something like that for Moz (but perhaps a bit less conspicuious) might be nice. Not that I'm complaining.
The latest nightly also lets me disable popups, status bar rewriting, and window resizing. I'm such a fan.