Hi, please see Security and passwords settings.

If you are not saving passwords within the above setting, you should clear the cookies for that site - Clear cookies and site data in Firefox.

You may also need to clear the cache - How to clear the Firefox cache.

If your question is resolved by this or another answer, please take a minute to let us know. Thank you.

A detail like a website remembering you (log you in automatically) is stored in a cookie. You can remove the cookies of a website to make the website forget about you.

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 with the mouse or cursor Down key
   do not click the mouse or press the Enter key
3. press the Delete key (on Mac: Shift+Delete) to delete the highlighted entry