Hi Jason, are they saved login suggestions or form history suggestions? The way you can distinguish those is that the saved logins have a key icon next to them, while form history suggestions do not.

To remove a form history suggestion, press the down arrow on the keyboard to highlight the item and them press Delete or Shift+Delete.

If you have an issue with saved logins from, for example, www.example.com showing up on mail.example.com -- the main domain is the same but the subdomain (left part) is different -- there is a setting for that:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

(2) In the search box in the page, type or paste signon and pause while the list is filtered

(3) Double-click the signon.includeOtherSubdomainsInLookup preference to switch the value from true to false if you only want suggestions for the exact match

More info on about:config: Configuration Editor for Firefox.

Any improvement so far?

jscher2000, thanks for the clarification. From what you said, what I'm trying to do is disable the form history suggestions entirely (instead of manually deleting each suggestion). Is this possible to do without disabling saved passwords? Thanks!

Yes, you can uncheck the "Remember search and form history" box in the History section of the Options/Preferences page. More info in this article: Control whether Firefox automatically fills in forms.