How to delete some of the form data in Firefox

Solution 1:

To delete saved form data in Firefox on a item-by-item basis:

• Highlight what you want to be deleted in the drop-down.
• Make certain that the drop-down remains on the screen.
• Press Shift+Delete to remove that entry.

Note: If you click an item from the drop-down, it populates the input box and the drop-down disappears. If you highlight the text in the input box and press shift+delete, the only result is that the input box is cleared. Doing this does not delete the saved form data.

Solution 2:

Highlight the entry to be deleted and press shift+delete.

Source: http://www.missiondata.com/blog/uncategorized/53/firefox-saved-form-data-frustrations/