Separate Issue; Your System Details shows;

Installed Plug-ins

Shockwave Flash 23.0 r0 Shockwave Flash 22.0 r0
Having more than one version of a program may cause issues. You must remove the older programs. Then get the current full installer.

Flash: Grab the uninstaller from here: Uninstall Flash Player | Windows Uninstall Flash Player | Mac

Then reinstall the latest version.

Note: Windows users should download the active_x for Internet Explorer. and the plugin for Plugin-based browsers (like Firefox).

Note: Windows 8 and Windows 10 have built-in flash players and Adobe will cause a conflict. Install the plugin only. Not the active_x.

Flash Player Version: 23.0.0.162 Flash Player (Linux) Version 11.2.202.635

https://get.adobe.com/flashplayer/ Direct link scans current system and browser Note: Other software is offered in the download.

https://get.adobe.com/flashplayer/otherversions/ Step 1: Select Operating System Step 2: Select A Version (Firefox, Win IE . . . .) Note: Other software is offered in the download.

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).

Is the problem still there?

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.

Unfortunately the issue still exists in safe mode. It appears the logins.json file in my profile does exist and is intact. The new Firefox version just cannot read the file.

could you go to the firefox menu ≡ > help ? > troubleshooting information, copy the contents of that page and paste them here into a reply on the forum? this might give us a clue what is going on...

My profile contains the following non-folder files:

storage.sqlite times.json webappsstore.sqlite webappsstore.sqlite-shm webappsstore.sqlite-wal xulstore.json addons.json blocklist.xml compatibility.ini content-prefs.sqlite cookies.sqlite cookies.sqlite-shm cookies.sqlite-wal extensions.ini extensions.json formhistory.sqlite key3.db logins.json mimeTypes.rdf parent.lock permissions.sqlite places.sqlite places.sqlite-shm places.sqlite-wal pluginreg.dat prefs.js search.json.mozlz4 sessionCheckpoints.json signons.sqlite

key3.db and logins.json : These are the Password files.

Hello, was a Master Password setup in Firefox before upgrading to Firefox 49?

Turns out my company network has updated it's security to disallow password storage within browsers. This is not a Firefox issue.

Hi   !

As this is no longer a problem:
Would you be a dear and mark   your  last post as   Chosen Solution,   so others will know   ?
Thank you   !