Way to butcher the quote. In full it has nearly the opposite meaning and it's far more intriguing -

  I believe that Mozilla can make progress in privacy, 
  but leadership needs to recognize that current advertising
  practices that enable "free" content are in direct conflict 
  with security, privacy, stability, and performance concerns 
  -- and that Firefox is first and foremost a user-agent, not 
  an industry-agent.

I don't see how that's opposite

The author's point is threefold:

1) Firefox should be software that serves its computer user's interests.

2) The Mozilla corporation is pressured (to whatever degree) to turn Firefox into software that serves the entertainment and advertising and surveillance industry's interests.

3) Sometimes Mozilla bends to industry interests rather than user interests. This is a bad thing.

When you excerpted that quote, you changed the author's statement into:

"Firefox serves the interests of computer users, rather than industry titans."

Understand? :)

#2 comes from your own mind or other sources (DRM standards), not from the quoted material.

#2 comes directly from the quoted material:

"[Mozilla's] leadership needs to recognize that current advertising practices that enable "free" content are in direct conflict with security, privacy, stability, and performance concerns..."

Not to be crass, but read between the lines. All statements have context. That one sits in the context of a world where browser makers have spent many years removing infoleaks from their browsers, much to the chagrin of advertisers and surveillers.

Conflict arises because content isn't truly free. Someone pays of their free time or gets paid to produce by advertising or subscribers. Tools that deliver the content while bypassing payment will drive payment elsewhere or erode the incentive to produce.

The thing I don't understand: why not just make the "Do Not Track" switch set this, as well as sending the eponymous header? The user has stated an intent to not be tracked... so help them accomplish that!

(In the same sense, I'm surprised that "incognito browsing" windows don't implicitly download a Tor "component" and route through it, the same way DRMed <video> elements implicitly download the Adobe DRM component.)

The GNU IceCat web browser (derivative of Firefox) does that with Tor.

There are many caveats* to consider when routing through Tor. It would be a bad idea to just silently do so when the user engages private mode. Incorporating Tor as a 'super-private' mode or whatever would be great, but it should be possible to use normal private mode without it.

*In particular the information that you share with the exit node. Especially if you're not aware you're using Tor, it would be easy to share identifiable information.

I think it may still be in development so they haven't added a preference to the about:preferences dialog yet.

Seems like a nice feature. I just enabled it and there's some overlap with ublock origin.

That is, when I load some pages with tracking protection and ublock, the number of requests blocked by ublock is smaller (but still far from 0).

After looking at Firefox log, it doesn't seem this feature blocks anything that was not blocked by ublock. But this might be wrong, I only tested a few sites, and I have no idea about the internals of these tools.

More knowledgeable info would be appreciated.

Yep, people looked and it's using filter lists, just less of them.