Rated 5 out of 5 stars

Awesome add on. Thanks. Possible improvement. The private mode tab should be more obvious with a flag or a different color in the tab. It would be too very comfortable to be able open a new tab directly in private mode

This review is for a previous version of the add-on (0.1.0b4.1-signed). 

See https://github.com/Infocatcher/Private_Tab#styles for userChrome.css/Stylish styles.

About new tabs: I will try to implement this feature, see https://github.com/Infocatcher/Private_Tab/issues/10 for progress.

[Added at 2013-04-09]
See extensions.privateTab.makeNewEmptyTabsPrivate and extensions.privateTab.makeNewEmptyWindowsPrivate preferences in new version:
https://addons.mozilla.org/addon/private-tab/versions/0.1.0