Breaks too many sites, DuckDuckGo, Qwant and several others, even when those are whitelisted. The extension most likely includes browser-wide settings which remain active even if it is disabled for a given site.

The extension is praiseworthy and was adapted, as I understood it, from the Chrome extension, and maybe is that where sits the culprit.

One star because the extension is obviously not operational now, but five stars for the extension's very concern: privacy, anti-fingerprinting all in the scope of tracking, which is getting worse day by day.

So be kept up the improvable work.

EDIT with latest version 2018.5.7 : a TRUE progress!
DuckDuckGo, Qwant no longer break. The developer is reactive and obviously corrects, improves the extension according to feedback (and his GitHub page is the place to dialog).

Tough to deliver a rating when the racer is still a child. I believe more in sharing experiences than in ratings which anyway need to be explained. Because of my edit I'll keep 5 stars for the extension's purpose and switch from one to three stars, because I haven't tested yet enough sites in their relationship with the extension. Maybe 5/5 tomorrow or in the coming weeks?!

Anyway, I'm keeping now 'Privacy Possum' as it seems "operational", at least enough to bring more benefits than problems.