Tor beside anonymizing our location also make us unique as very few users actually use it on each webservice.

question is in what ways destination sites can detect Tor browser? for instance canvas protection is a sign of Tor browser and a simple script can exploit it. what other footprints can tell a website that user have Tor browser not a normal browser? and how we can modify Tor browser to hide these footprints and look like a normal firefox user?

Note: my question is for when user don't use Tor's socks proxy, but just Tor's enhanced browser directly or over an undetectable proxy ...

4 Answers 4


I do not think it is the intention of Tor to be undetectable, rather it is designed to make you indistinguishable from others.

According to this post in SO, a browser can be a TBB if it:

  1. Has a User-Agent of Mozilla/5.0 (Windows NT 6.1; rv:31.0) Gecko/20100101 Firefox/31.0
  2. Has a screen resolution that matches the browser window size (particularly if that size is 1000x800)
  3. Has a time zone of "0" (GMT)
  4. Has no plugins (navigator.plugins is empty)

As to the different ways of detecting browsers, there is now a paper from EFF that investigates the degree to which modern web browsers are subject to “device fingerprinting”. Based on this, they have developed Panopticlick tool that tests your browser to see how unique it is based on the information it will share with sites it visits.

  • @user9310 As you are a reputation 1 user: If this answer helped you, don't forget to click the grey ☑ at the left of this text, which means Yes, this answer is valid! ;-)
    – Ron
    Commented Sep 10, 2015 at 16:23
  • On Mac, the browser does not default to full screen. And if I click full-screen, I get warned that this will identify my platform to servers. Which isn't true, because if a server tries to fetch the size, TBB won't answer without first asking permission. From all that, I wonder: Is it not possible to change the default window size from fixed to "some random size less than full screen but not too small to be irritating"? (in other words, different for every window.)
    – WGroleau
    Commented Oct 9, 2015 at 16:44
  • @WGroleau, a fixed default window size is more anonymous than a random size. If the default size is fixed, you can't tell one user of the TBB from another; in contrast, if the default window size varies randomly by only 100 pixels in either direction, there's only a one-in-ten-thousand chance that two visitors with the same window size are different people.
    – Mark
    Commented Dec 8, 2015 at 2:42
  • It will vary by N pixels from X and Y in two directions, plus X & Y are different for different computers. But I see the point. N² is, however, a pretty big number. How many Tor users are there? Presumably at least as many as there are relay nodes.
    – WGroleau
    Commented Dec 8, 2015 at 17:21
  • 1
    @WGroleau "if a server tries to fetch the size, TBB won't answer without first asking permission", it absolutely can fetch the size without user prompting.
    – cacahuatl
    Commented Jul 12, 2016 at 11:43

how we can modify Tor browser to hide these footprints and look like a normal firefox user?

You cannot, some of Tor Browsers changes are hard coded patches. Trying to undo some of them by configuration will leave you still being detectable as Tor Browser but not looking like a normal Tor Browser user (I.E. more unique and more trackable).

For more information see: https://tor.stackexchange.com/a/11705/12737

For what changes Tor Browser makes and why it makes them see: https://www.torproject.org/projects/torbrowser/design/


TBB-bundled FireFox, or standalone FF instance - they ARE browsers. And can be tricked to track you outside their own settings. Use a virtual machine hard-routed through Tor if you need to be undetectable. Use a new one(virtual machine with the browser) if you need to change your representation on the other side. But remember - never login into anything, because it will bind your different virtual machines by the account you've just logged in =)


using the TOR browser doesn’t mean we are fully protected, by avoiding it using in full-screen mode and other small precautions might provide minor exposure to tracking compared to Firefox.

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