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.)