In stackoverflow.com, I have two logins:
email as firstname.lastname@example.org,
OpenID via facebook.
I started with 1) but later found 2) is quite convenient.
After login via facebook, click "logins":
Now, my office network blocked facebook, so I have to login Stack Overflow using the 1st account.
However I can't login using "email@example.com" anymore! It says "No account with this email found"!
How could I link my 2 accounts together, so that I can login via my email account in office?