[jeffcutsinger]

> DNT, on the other hand, is something all Firefox users will have enabled by default

It's opt-in. My guess is that the gap between people willing to install an add-in and people willing to dig into their settings and check a box is not large.

[eggbrain]

From the article:

  ...That would leave Firefox in a permanent state of blocking advertisers' cookies by default.

Default means this feature would be an opt-out feature, not an opt-in feature. Since Firefox now autoupdates, that means soon most Firefox installs would have this enabled by default without any user input.