Does it already have a password listed?

Type about:preferences#security<enter> in the address bar. Look under Logins,

Note: For Firefox 56+ its; about:preferences#privacy Look under Forms & Passwords +++++++++++++++++++++++++++++++ Turn on Remember Logins. To check the passwords you have listed, press Saved Logins.

Press the Exceptions button and see what's inside.

Thanks. But I don't have any exceptions listed, and as I said I know how to review my saved logins. The issue is that I don't know how to edit those saved logins, or add to them.

Some websites do not use a form, but only use two input fields and a submit button to submit these fields via AJAX or otherwise use a setup that Firefox doesn't recognize as a login form.

In theory you could try to save a name and password on another website and then edit this record in logins.json and modify hostname and usernameField and passwordField. You can double-click name and password field in the Password Manager or use the right-click context menu to edit these fields. I've never done this myself, but at least this way you have the username and password saved in the Password Manager if Firefox offer to fill. This file is in JSON format, so you need a basic understanding of how this format works and make sure not to break this file. You can set this pref to true to get a log in the Browser Console.

• signon.debug = true

That's an interesting strategy, and thanks for telling me that logins.json is where those logins are stored. But how do I edit that file? In vi, it comes up as ONE very long line. Certainly a lot of potential for breaking it.

Where in Preferences do I find signon.debug? When I go to about:preferences, I don't see it.

You can inspect and modify prefs on the about:config page. You can open the about:config page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue.

• http://kb.mozillazine.org/about:config

Yes, the logins.json is one long line without any line breaks although linefeed like used in HTML should work. I've edited the file as a test and added a line break (%0a) after "}," to make each entry {"id":xx start on a new line and that works.

You can test the modified file by opening the file in a Firefox tab and have the builtin JSON viewer handle the file.

• https://developer.mozilla.org/en/Tools/JSON_viewer

Thanks. But "about:config" isn't Preferences. At least not the Preferences you select in the menu button. Good ideas about editing the JSON file. Too bad the JSON viewer isn't a JSON editor!