Yeah, like DNT is useful in FF. Is it on a right mouse menu so you can easily allow or deny tracking per site? On a menu perhaps? Heck no, it's a global checkbox in preferences. Wait, didn't that option used to say "Don't accept cookies" or something and they just renamed that checkbox?
Ah yes, check out this old screen shot in the pre DNT version of FF:
The current implementation is just worthless lip service IMO and as you can plainly see, we actually lost some functionality in this feature so it appears to be less useful than it once was.
Which brings up a another silly question. If the browser isn't accepting the tracking cookie, which has already been available as an option for a long time already, what in the heck does the website like Twitter need to do to implement DNT?
Nothing. Absolutely nothing.
Unless they are tracking by IP regardless of the cookie which is kind of hard to do with all the NAT routers in use behind the cable modems these days, but it's close enough.
Mostly just more worthless PR to confuse the users.
Time for everyone to jump on the FUD-wagon as it's going to be a wild ride of confusing uselessness and meaningless platitudes for the masses to wade through as all the marketing mayhem commences and we lose functionality under the guise of enhanced privacy.