See Reset your Primary Password if you've forgotten it and http://kb.mozillazine.org/Master_password If using the chrome url (chrome://pippki/content/resetpassword.xul) doesn't work then delete key3.db and signons.sqlite (Firefox 3.5) and all signons#.txt files (if any exist, Firefox 3.0 uses signons3.txt) in the Profile_Folder.

You need to set a new Master Password after renaming or deleting key3.db and you lose all your currently saved passwords.

I have the same problem with Firefox Version 3.6.3. But I do not want to set a Master Password and I go into Firefox Preferences, Security, and Un-click the "Use a Master Password" and then a box appears, asking for Current Password. So, I enter it and from the box's, Cancel and REMOVE, REMOVE is not highlighted so I can't select that and have to select Cancel and can't get anywhere. What do I do to get the Master Password popping up everytime asking for it when I am on a website and have to put in a password for it at a website?

If you want to remove the Master Password then click the Change Master Password button and supply the current Master Password and leave both fields for the new Master Password blank and click OK. If you do not know the current Master Password then see my above post.