Rated 4 out of 5 stars

Simple, and effective. Does what it claims and thus what it is supposed to do without unnecessary whistles and bells. Two suggestions though
1) It would be great if one could set the address for the new tab.
2) I like to make an private tab and 'pin' it since I use it often. That way I can easily switch to the tab when I want to browse privately for a sec. It would be great if this new private tab had an 'forced favicon' like, for example, the purple mask!

These are just my own ponderings though, this is one great addon that from now on comes with all my Firefox installs. This is one of those addons that should be integrated by Mozilla.

This review is for a previous version of the add-on (0.1.6.1-signed). 

> 1) It would be great if one could set the address for the new tab.

I've created an issue:
https://github.com/Infocatcher/Private_Tab/issues/125


> 2) I like to make an private tab and 'pin' it since I use it often. That way I can easily switch to the tab when I want to browse privately for a sec. It would be great if this new private tab had an 'forced favicon' like, for example, the purple mask!

See https://github.com/Infocatcher/Private_Tab#styles and https://github.com/Infocatcher/UserStyles/tree/master/Private_Tab_icon
Example style: https://gist.github.com/Infocatcher/7772476