Rated 5 out of 5 stars

Looks nice but how can i open private tab via command line and navigate url ?

This review is for a previous version of the add-on (0.1.3.1-signed). 

See my reply here: http://forums.mozillazine.org/viewtopic.php?p=13001267#p13001267

[Added later]
Since version 0.1.4 ( https://addons.mozilla.org/addon/private-tab/versions/0.1.4 ) can be used
firefox private:///#https://addons.mozilla.org/
(and all other URL-related command line things)