Firefox stores previous form entries and previous search entries as part of its autofill feature. You can disable that feature and clear past entries as follows:

To disable the feature: Open the Privacy panel of the Options dialog:

"3-bar" menu button (or Tools menu) > Options > Privacy

If the selection is "Firefox will: Remember history" change it to "Firefox will: Use custom settings for history". This should reveal a number of checkboxes, etc.

Uncheck the box for "Remember search and form history"

To clear all past entries: Use the Clear Recent History feature.

Important: be careful to deselect all other kinds of history so they are not permanently deleted.

Either

• "3-bar" menu button > History > Clear Recent History
• (menu bar) History > Clear Recent History

Expand the lower part of the dialog (if needed) to show checkboxes for different kinds of personal data, and uncheck all the categories other than "Form & Search History"

At the top of the dialog select the time range "Everything" and then click OK.

Success?

What search bar are you referring to?

• searching via the location bar
• search bar on the Navigation Toolbar
• search bar on the about:home page or about:newtab page
• other search bar (e.g. on a web page)

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:

• https://support.mozilla.org/kb/remove-recent-browsing-search-and-download-history

Note that clearing "Site Preferences" clears all exceptions for cookies, images, pop-up windows, software installation, passwords, and other website specific data.

jscher2000 said

... If the selection is "Firefox will: Remember history" change it to "Firefox will: Use custom settings for history". This should reveal a number of checkboxes, etc. ...

Right! Have to be custom. Thank you.

Note that the "Use custom settings for history" selection allows to see the current history and cookie settings, but selecting this doesn't make any changes to history and cookie settings. Firefox shows "Use custom settings for history" as an indication that at least one of the history and cookie settings is not the default to make you aware that changes were made. If all History settings are default then the custom settings are hidden and you see "Firefox will: (Never) Remember History".

cor-el said

... "Use custom settings for history" selection allows to see the current history and cookie settings, but selecting this doesn't make any changes to history and cookie settings. ...

That's right, mate. Thanks for response.