If I go to MathOverflow from another SE site by clicking on the link in “Your Communities” under the right-most menu on the top-bar, I do not end up with the usual https://mathoverflow.net, but with a strange URL such as


The string is different each time. The same happens when I go from MathOverflow to MathOverflow Meta or vice versa, but not when I go to any other SE site.

What is the meaning of this? Is it a bug?

EDIT: It’s not just MathOverflow. It also happens when I go from other sites to Server Fault or Ask Ubuntu, so it appears to affect all Stack Exchange sites with their own domain. Since it is not MO-specific, I reposted the report on Meta SE.

  • 2
    $\begingroup$ Can't reproduce this in my office (RHEL 8.5, Chromium). What browser do you use? Have you tried a different device/browser/incognito mode? Is Mercury in retrograde, have the goats bleated twice before the sacrifice? Have you tried to blame caching? $\endgroup$
    – Asaf Karagila Mod
    Sep 23, 2022 at 13:37
  • $\begingroup$ This is Firefox 105.0 on Linux. Reloading the cache, restarting the browser, logging out and in, and trying private mode, made no difference. Now I checked that Chromium 105.0 does it, too. $\endgroup$ Sep 23, 2022 at 14:06
  • 7
    $\begingroup$ So, as answered by VLAZ on Meta.SE, it turns out this is a Google Analytics cross-domain tracking parameter, and it goes away if you disable performance cookies. $\endgroup$ Sep 23, 2022 at 15:04
  • 2
    $\begingroup$ Ah. That makes sense. I'm not used a browser without an ad block for years now. $\endgroup$
    – Asaf Karagila Mod
    Sep 23, 2022 at 15:14


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