Firefox keeps suggesting usernames, even though I have disabled the default password manager

I use LastPass as a password manager. I have disabled Firefox's inbuilt password manager.

LastPass has only one entry for the site I'm visiting, but Firefox still suggests many different usernames:

How do I stop Firefox from suggesting unrelated usernames?

Solution 1:

The feature you're seeing is not related to the password manager but rather form data. Check History, change it to "Use custom settings for history" and disable "Remember search and form history" if you really don't want that feature.

This will also disable the suggestion feature for other form types. For example you might have common search terms that won't be available as a quick select anymore or your address and so on.