Does private mode enable "Do Not Track" (DNT) on popular browsers?

Question

I have found quite a lot of requests in my web server logs coming from various browsers (IE, Firefox, Chrome) with Do-Not-Track header enabled.

I suspect that these users have not enabled Do-Not-Track manually because it is not a popular and widely known user setting, in my opinion, but rather that it's being enabled for them when they use each browser's "private mode".

So does "private mode" actually enable Do-Not-Track? on popular browsers

Answer 1

I quickly tried whether private browsing turns on DNT (i.e., includes a DNT: 1 header) when "do not track" was not already enabled in the preferences.

• Firefox 39 (Android): no
• Firefox 41: no
• Chrome 43 (Android): no
• Chrome 45: no
• Opera 12.16: no
• Internet Explorer 11: yes
• Safari 6/7 (Mavericks): yes (according to docs)
• Safari 8 (Yosemite): yes (according to docs)
• Safari 9 (Yosemite): yes (tested by OP, on Safari 9.0 (10601.1.56.2))
• Safari (iOS): yes (implied by docs)