Let {Site1,Site2}={MathOverflow,xxx.Stackexchange} (in either order, with xxx representing "superuser" or "chess" or any of dozens of others).

I want to be logged into Site1 as Name1 and simultaneously (in another window in the same browser) logged into Site2 as Name2.

This is normally impossible. As soon as I log into Site2 as Name2, Name1 gets kicked off Site1.

But I know there's a way around this, because I've done it before. You first log in to one site using one name, then delete some carefully selected cookies, then log into the second site using the other name. This logs you into each site under the appropriate name, and typically things are good for a year or more.

Then something happens, you log out of one site or the other for some reason, and you have to go through the whole process again. And every time, I forget the process. I remember that it really matters which site you log into first, and that it really matters that you delete exactly the right set of cookies (neither too few nor too many).

I usually do this by time-consuming trial and error. Can someone save me the effort by reminding me of the secret trick for all this?

(I'm using Google Chrome if it matters.)

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    $\begingroup$ On Meta Stack Exchange there is this question: How can I log into two different accounts on two different sites now (July 2015)?. (Although I don't think the answer there tells you something you don't already now.) Maybe this Federico Poloni's question might also be useful: Where and how is the authentication cookie stored with the new authentication system? $\endgroup$ Commented Nov 9, 2019 at 23:30
  • $\begingroup$ @martinsleziak : but I am certain (because I once fully understood all this) that the answer is very different depending on whether or not one of the sites is MathOverflow. Which will tend to render any answer that doesn't specifically mention MO irrelevant. $\endgroup$ Commented Nov 10, 2019 at 0:32
  • $\begingroup$ Oh yes, I vaguely recall that sites which have a separate domain (such as Super User or MathOverflow) are treated differently: Active login not recognized on Super User and other posts linked there. $\endgroup$ Commented Nov 10, 2019 at 1:53
  • $\begingroup$ Aha! I solved the problem. As before, you have to do everything in the right order (log into one, out of one, into one, etc) and you have to delete the right cookies in the right order --- and as before, I finally hit on the right pattern by trial and error, and failed to keep track. BUT: For a long time, nothing worked. The key was, in the browser settings, to "Block third party cookies". After that, one of the twenty patterns I was trying worked, though before that none of them did. $\endgroup$ Commented Nov 10, 2019 at 2:35
  • $\begingroup$ Although --- blocking third party cookies should not be necessary, as I've never blocked them before, and everything has been working fine for a long time. The present crisis occurred when I joined one additional stackexchange site and suddenly nothing worked anymore. It's fixed now with third party cookies blocked, but I'd still sure like to know how I solved this problem before without recourse to that. $\endgroup$ Commented Nov 10, 2019 at 2:37
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    $\begingroup$ You can log on to Site2 on a different browser or in incognito mode on chrome (but then you'll have to login again each time). $\endgroup$ Commented Nov 10, 2019 at 3:38
  • $\begingroup$ @FelipeVoloch : Yes, that's precisely what I'm trying to avoid. $\endgroup$ Commented Nov 10, 2019 at 4:39

1 Answer 1


The procedure appears to be:

1) Have third-party cookies turned off.

2) Log into MathOverflow with the desired account.

3) Clear all cookie data for all sites ending in stackexchange.com

4) Log into ***.stackexchange with the desired account.

The order very much matters.


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