According to the tracking preference expression (TPE) spec, the doNotTrack property should be on the window object, not the navigator object. This is because it is possible the user has different DNT settings for different sites. http://www.w3.org/TR/tracking-dnt/#js-dom

What do other browsers do?

No it should not. I commented to that effect on the public mailing list. window and navigator have one-to-one mapping and per-site stuff is fine on navigator. See service workers. I recommend WONTFIX.

Anne: Why don't we leave this bug open until your concern gets discussed and hopefully resolved in the spec? While I agree with you in principle that it should be on navigator, it seems kind of counterprodutive to differ from safari and IE on this. http://compatibility.shwups-cms.ch/de/home?&property=doNotTrack reports that IE 11 and safari 7 use window.

The comments annevk mentions are here: http://lists.w3.org/Archives/Public/public-tracking-comments/2014Apr/subject.html

According to the recommendation [http://www.w3.org/TR/tracking-dnt/#js-dom] it should live on navigator so, I agree with Anne, we should mark this as WONTFIX The landscape at the moment is: On navigator [Firefox, Chrome, Opera] On window [IE, Safari]