Rated 5 out of 5 stars

@jsmithson:

"Question: In the newest Firefox 42.0, they've added some anti-tracking features to private windows. I assume that works in private tabs too, but I'm not sure. Does anybody know?"

Tracking protection does not work in private tabs. It's easy enough to check, and I just did: Load a page in a private window. Click the address bar icon. You will see "Tracking Protection" there. Now load a page in a private tab. No "Tracking Protection" entry.

This review is for a previous version of the add-on (0.1.8.1). 

Indication doesn't work (and this should be corrected, of course), but looks like tracking protection is also enabled for private tabs (you can check this through built-in developer tools, Network tab).