First, In the event that the passwords information is lost, you should record all information in a separate text file somewhere else on your hard drive, or written down. You can easily copy and paste if you need to do so. If you are concerned about someone else looking at that file, you can compress it using a password.

When was the password added or last modified?

Many site issues can be caused by corrupt cookies or cache.

Warning ! ! This will log you out of sites you're logged in to. You may also lose any settings for that website.

• Delete cookies to remove the information websites have stored on your computer {web link}

• How to clear the Firefox cache {web link}

If there is still a problem, Start Firefox in Safe Mode {web link} by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh). Did this help?

While you are in safe mode;

Try disabling graphics hardware acceleration in Firefox. Since this feature was added to Firefox it has gradually improved but there are still a few glitches.

How to disable Hardware Acceleration {web link}

Thanks, the password was entered at least six months ago. Matter of fact, i used it last night, this morning it was gone. It's interesting that it can be caused by a corrupt cookie or cache.

It creeped me out so I ran a bunch of virus scans, all were clear so i ran an offline scan and it picked up a trojan (severe rating) where it can access your system remotely and record keystrokes. The offline scan quarantined it and i removed it. The file it was located in was an old download so I don't think it had been active, at least there was no evidence of it, but I changed important pw's just in case.

If it was nothing, I'll be glad, and glad it pointed me to do in depth scans.

Put that password back and keep an eye on them.

https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save

Note: Some software, like Advanced SystemCare with Surfing Protection, can protect files in the Firefox profile folder against changes. If you have such software then check the settings or uninstall this software.

I do use Advanced SystemCare, and ironically the trojan was located in one of their downloads to upgrade but it was an old version #9, as I am currently running 12 so it's been there for quite some time.

On some sites I can see the activity or will be notified if someone tries to sign in with a different browser and there hasn't been anything. Keeping my eye on it though. If they were stealing info, why delete a user name and pw that someone is going to notice, it's a 2 step deletion. At first I thought it might have been an error to delete it but, it's kind of hard to do that when it's 2-step. I don't know, I hope I got rid of it before anything happened. At times when my system seemed to be eating up a lot of RAM, I always look at my processes, but there was never anything that was questionable, usually it was Firefox eating it all. I hope it's just a corrupted cookie.

Unless you are using sync, something external should not be able to change your data.

You would need a copy of logins.json and key4.db where logins.json contains this lost password to recover it.

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

If you use Sync and include logins (passwords) then you can check this login data on other connected devices.

Yes, I am using sync. Just in case, yesterday I changed my pw and even email address on my firefox account. It automatically logged off my other device and had to log back in.

Only one pw was missing which i keep somewhere else to retrieve so that's not the problem, it was just weird that it was gone from the list.

After reading more about the Trojan, there is conflicting information about it but Windows Defender removed it and Malwarebytes didn't find anything.

https://malwaretips.com/blogs/remove-misleading-win32-vigorf-a/

I didn't experience any of the issues that are described. Malwarebytes had been running previously and quarantined other found threats. You can't be too careful, but I think maybe the missing pw and username was a fluke. Knowing it can be caused from a corrupt cookie or cache file is helpful. Thanks.