Rated 5 out of 5 stars

Small, simple, no restart required and it does what it should. Very good :).

Only one thing: It doesn't work with e10s until now. I can't open links in a new tab or in a new private tab if this add-on is enabled.

Edit: Oh, okay, thanks for that info. I leave the note here if someone else is experiencing the same issue. But as e10s is in development it's still completely worth five stars ;-).

This review is for a previous version of the add-on (0.1.7.3.1-signed). 

This is known issue about e10s:
https://github.com/Infocatcher/Private_Tab/issues/162