Environment: Windows 10 Pro ver 1903 64-bit, with Firefox Browser 70.0 - Option to save user-passwords is enabled, Password Manager not enabled.

My home network modem and router share the same user-password, but have different numerical addresses. Firefox remembers for the modem only. The router, I always have to fill in manually. It's a nuisance. I tried Tools | Web Developer | Inspector, but no elements show up on the router's blank login page. I fill in Firefox's user-pass pop-up box dutifully but the log-in never takes for the second round. The obvious fix - change the password in the router, I know, but if my Android tablet can do it, why can't Firefox Quantum?? I've scoured the web and various KBs, but there's not much about it by manually editing about:config or adding it to user.js. I prefer not to install third-party extensions or store my user and passwords off-site. For an in-house solution, I'd be very grateful. I don't mind if it's complex for a non-coder. I need this. Thank you.