by Menu ->Privacy and Security there should be a option to clear autofill lists

You can use these steps to remove saved items from an autocomplete drop-down list.

1. click the (empty) input field on the webpage to open the drop-down list
2. highlight an entry in the drop-down list with cursor Down key
   do not click the mouse or press the Enter key
3. press "Delete" or "Shift+Delete" to delete the highlighted entry

Note that hovering with the mouse doesn't work.

• https://support.mozilla.org/en-US/kb/remove-websites-address-bar-suggestions

I stated that this did not work.

Only see options to clear addresses and credit cards. Not other auto fills.

privacy.clearOnShutdown.formdata

open a new tab location about:config search that if not exist create, set to true

As the setting suggests this will happen every time you exit firefox