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

See also:

• Tools > Options > Security: Passwords: "Saved Passwords" > "Show Passwords"

• https://support.mozilla.org/kb/password-manager-remember-delete-change-passwords

rexinewj said

when logging into gmail, previous sign in emails show up. how can this be prevented?

thanks to the many responses but the one I did find that works is the following: Prevent Firefox from storing form entries If you don't want Firefox to remember what you've entered into form fields, you can turn off the auto form fill feature: 1. Click the menu/tools button and choose Options. 2. Select the Privacy panel. 3. In the drop-down menu next to Firefox will:, choose Use custom settings for history. 4. Remove the check mark next to Remember search and form history. 5. Click OK to close the Options window. Disabling form history also prevents Firefox from storing search history for the Search bar in the Navigation Toolbar.