Image.

You need to make the changes in FF settings and look there to see what else is keeping a cache of the input and you have to clear those results to remove them. Also it does help if posted in english.

You can use these steps to remove saved items from an autocomplete 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 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

Note that hovering with the mouse no longer works.