Go to Tools >> Options >> Security >> click on Saved passwords then select the login and delete it by clicking on the button at the bottom of window.

• Password manager

The password is attached to the login name - I need to delete that incorrect login

You can use these steps to remove saved (form) data from a drop-down list:

1. click the (empty) input field on the web page to open the drop-down list
2. highlight an entry in the drop-down list
3. press the Delete key (on Mac: Shift+Delete) to remove it.

• http://kb.mozillazine.org/Deleting_autocomplete_entries

thanks - problem now solved