Please do the following.

1. Click the orange Firefox button, go to Options | Options and then click the Security button.
   
   
2. Next, click the "Exceptions" button and then remove the site you don't want to save a password for in there.

Sorry! Your reply is regarding add-ons; but my question is regarding a site.

In the menu I described, you'll see the list of sites which have been added to the Exceptions list, that is to say, those sites which normally require a login, but which the user has chosen not to include in the saved password list. This has nothing to do with Add-ons. See screenshot.

Sorry! Your reply is completely irrelevant to the point. Let me explain again my problem. I keyed-in a certain URL and a drop-down window opened which warned me that "this connection is untrusted". When I clicked the "I understand the risk", it asked me to "add exception". I did so. Now I want to remove the exception, but I could not. Can you suggest a solution?

You can see if you can find the exception here:

• Tools > Options > Advanced > Encryption: Certificates > View Certificates : Servers

Rename or delete the file cert_override.txt (cert_override.txt.old) in the Firefox Profile Folder to remove all permanent exceptions that you have saved.

Thanks! This is exactly what I was looking for. Thanks once again.

You're welcome