I use firefox (mainly on linux but also on windows), and I have it set up to delete cookies and browsing history every time I exit. Despite this, every time I come to tex.stackexchange.com, I am recognized a few seconds after I connect. How is this done without cookies?

  • Do you log in to a different SX site before you come to TeX.SX? – Caramdir Feb 20 '11 at 0:01
  • No, it happens even if I come here first. In case it matters: I never actually log out, I just shutdown firefox. – Phil Hirschhorn Feb 20 '11 at 0:14
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    How do you login? Using Open Id I assume? It could be some flash based cookie which isn't deleted by firefox. – Martin Scharrer Feb 20 '11 at 0:18
  • Yes, I had to create one of those OpenId thingies to register, and I seriously don't understand what that is. I've heard the phrase "flash cookie", but don't know what that is either. – Phil Hirschhorn Feb 20 '11 at 0:34
  • I googled "flash cookies" and went to a macromedia web site that allowed me to delete all flash cookies from all sites. I then shut down firefox, started up firefox, came here, and I was still recognized. Weird... – Phil Hirschhorn Feb 20 '11 at 0:51
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    Actually, this should probably be asked on meta.stackoverflow.com. Why isn't there a migration path to meta.SO? – Caramdir Feb 20 '11 at 1:41

Traditional browser cookies are by no means the only way to store tracking information. For example there are also cookies stored using Adobe Flash (use this site to configure flash storage).

EDIT: My original guess turns out to be wrong. They seem to use HTML5 local storage, as described in a blog post. One way to somewhat reliably remove tracking information is the BetterPrivacy Firefox addon (I haven't tested that extensively, but it seems to work for stackexchange).

  • I already use noscript, so I tried blocking quantserve and google-analytics, shut down firefox, restarted firefox, came here, and it still recognized me. I'm starting to think there's someone hiding in my closet. – Phil Hirschhorn Feb 20 '11 at 1:07
  • @Phil: interestingly it does that for me now too. Anyway, as I said there are lots of methods for tracking users. – Caramdir Feb 20 '11 at 1:14
  • Aha: Private Browsing. I started firefox, started private browsing, and I was not recognized here. When I turned off private browsing and returned here, I was recognized. I still wonder what's being stored where... – Phil Hirschhorn Feb 20 '11 at 1:14
  • @Phil: see updated answer. – Caramdir Feb 20 '11 at 1:34
  • @Caramdir: Lovely! Thanks very much. – Phil Hirschhorn Feb 20 '11 at 1:46
  • @Phil, @Caramdir, from diveintohtml5.org/storage.html: Unlike cookies, this data is never transmitted to the remote web server (unless you go out of your way to send it manually). – Hendrik Vogt Feb 20 '11 at 7:05
  • @Hendrik: As long as the website can access it with javascript, it can send it to any place it likes. – Caramdir Feb 20 '11 at 16:46
  • @Caramdir: So you're saying the info at that link is misleading (or plain wrong)? – Hendrik Vogt Feb 20 '11 at 21:30
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    @Hendrik: it says '[html5 local storage] isn’t transmitted to the server', meaning that unlike a cookie it isn't sent to the server on every request. However, it must be accessible with javascript (otherwise it would be pretty useless) and it is possible to make arbitrary requests to the server using javascript (a feature that is used extensively in 'web2.0' sites). So there is nothing preventing the javascript on the site calling example.com/tracker?id=<id from local storage>. – Caramdir Feb 20 '11 at 22:02
  • Chrome's Incognito mode by default wipes all state at session end, including HTML5 local storage. – Charles Stewart Feb 21 '11 at 9:30
  • @Caramdir: Thanks for expanding. However, I'm still puzzled. Why on earth do they say "Unlike cookies, this data is never transmitted to the remote web server (unless you go out of your way to send it manually)"? I start tending to "plain wrong" ... – Hendrik Vogt Feb 21 '11 at 19:58
  • @hendrik: it is correct from the developer point of view. – Caramdir Feb 21 '11 at 20:11

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