I found that this from the article rather telling:

"A feature for more than a privacy-centric niche. We sometimes think that privacy protection tools are valuable to only a small portion of privacy-centric users (3-8% depending on the study) or general users at specific moments (for example, using the private browsing window). It is noteworthy how many of the participants found value in tracking protection."

I constantly hear from friends (especially Chrome users) that no one cares about tracking on the internet. I think it is uplifting to hear that many of the participants found value in tracking protection.

Yes, it was interesting from our perspective also. For some participants, the use of the tracking protection feature brought attention to tracking. Further, at least two of the participants described how they researched tracking as a result of using the tool.

It's easy for users to not care about some they can't see. The participants' comments about visible vs invisible aspects of tracking were telling.

Maybe this came up already, but how does the tracking protection work? Does it use a blacklist like uBlock, or a whitelist like Privacy Badger?

The page links to https://wiki.mozilla.org/Polaris#Tracking_protection "The current blocklist is powered by Disconnect."

This page has a link to a Python script to dump the contents of the list file:

https://wiki.mozilla.org/Security/Tracking_protection