Oh, and it does this on multiple devices, Windows and Mac.

Do you have it set to forget cookies on restart? (In Settings->Privacy & Security under Cookies: "Delete cookies and site data when Nightly is closed" checkbox.) Do you have any privacy extensions which might be doing something similar?

Nothing is set to forget cookies at any time. I did notice something while I was looking. "don't enable https" was selected. I changed that to "always enable https". We'll see if that changes anything.

Thanks for the info. Is "Don't enable https"/"Always enable https" actually "HTTPS-Only Mode"? That shouldn't affect remembering logins, but let's see.

You could also create a second profile using about:profiles, and then see if it has the same problem. If it doesn't, then we know it's *something* set in your profile. Once we know that, we can work to figure out what.

(Have you every set any prefs via about:config? In general that's unsupported behavior, and depending on the pref it can really mess things up unless you know exactly what it does (and that someone has kept it working properly)

I went to about:config, and found a lot of things I'd customized. I got excited for a few minutes, and closed Firefox and reopened it. I then navigated to one of the places that refuses to save Firefox logins for me. Nope, didn't help. I still don't have whatsapp, so I can't get a text through there, and there's not a snowball's chance in Miami I'm giving them my photo ID to verify my identity. So, no, resetting those settings didn't do anything. I have a secondary account, and tried that. Another nope. Whatever it is seems to be Firefox-centered.

Thanks. Can you try a fresh profile? about:profiles, Create a New Profile, then Launch profile in new browser. (I advise after launching it to quit the old browser to avoid confusion).

Then log in to a site and authenticate, and check "remember this device". Quit the browser, reopen. You should be in your original profile; go to about:profiles again and Launch the new profile again. Then check to see if it remembers you or forces you to authenticate with TFA again.

I assume the sites in question use "Remember this device" to avoid asking sending a code, using an Authenticator app, etc. Which sites do you remember this happening with?

Firefox Nightly or release?

Note that I've frequently seen that my device gets forgotten either after <X> time (month, week, etc), or when the browser version changes for some (and we release new Nightlys every day, and new Release browsers at least once a month, but usually 2-3 times (for XXX.0.N releases)

Thanks again!