Is it an address, credit card info, or just an item in the text box?

I want to delete login usernames. One was spelled wrong and another is obsolete.

So it's in Passwords.

I don't use saved passwords at all. Firefox confirms 'No saved passwords'. Autofill somewhere saves all kinds of text that has been entered in web page forms. In my Firefox this including login usernames, email addresses, street addresses etc. That is the autofill data I need to edit please.

So try to remove it using the Delete key.

Hello,

• Go to a form with your item appearing.
• Use the ↓ (down arrow) key to highlight the incorrect entry.
• Press Shift + Delete (on Windows/Linux) or Shift + Fn + Delete (on macOS) to remove it.

There is Form History Control add-on but it doesn't work for already entered items. Manage form history entries (search, edit, cleanup, export/import) and easy text formfiller. Auto-save text entered in any form while typing to allow fast recovery when disaster strikes.

This add-on now uses the new mandatory WebExtensions API which no longer offers access to Firefox's built-in formhistory database. To overcome this limitation this add-on will create and maintain its own private formhistory database which initially will be empty.

Many thanks @Logosor Shift+Delete was the essential info I needed!

Previously I tried plain Delete (suggested elsewhere) but that does not delete already saved autofill items in my Firefox.

Also glad to know about the new add-on. I will look at it later, thanks again.

I've already tried the extension Form History Control. I found it good. Maybe I'll reinstall it.