The weird logins

My latest workstation is spooky. Almost each time I try to login to any of my web accounts, I'm logged into some random account that doesn't belong to me! I initially though it was the host site that was erring. But many sites behaving this anomalously rules out that possibility.Then I assumed my primary browser (Firefox) was playing tricks. But IE was behaving just as erratically. Sometimes even logging out fails. While the confirmation message is
shown, returning to the login page automatically gets me logged
in...and I never save my passwords. Thankfully, not all sites misbehave this way.

My conclusion: There are invisible/spiritual forces haunting my workstation.