Hello rs27, highlight/touch, DON'T Click the username you want to delete and then click delete on keyboard.

thank you

Also see

• Control whether Firefox automatically fills in forms

Thank You! That has frustrated me for a long time.

you are welcome

That doesn't work for me. Here's a different answer: Deleting individual form entries If you want to remove one of your previous form entries from Firefox's history:

   Click on the form field and press the down arrow key to display all the saved entries. You may type the first few letters of the entry to limit the number of entries displayed.
   Use the down arrow key or the mouse pointer to highlight the entry you wish to delete.
   Press Shift+Delete. The entry will be removed. 

(from https://support.mozilla.org/en-US/kb/control-firefox-automatically-fills-in-forms#w_deleting-individual-form-entries )

Hello geoffrey.landis, it is the same..... Shift+Delete is for mac, Delete for all other os.

thanks