Separate Issue; Your System Details shows;

Installed Plug-ins

Shockwave Flash 28.0 r0 Shockwave Flash 12.0 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:

http://helpx.adobe.com/flash-player/kb/uninstall-flash-player-windows.html Uninstall Flash Player | Windows

http://helpx.adobe.com/flash-player/kb/uninstall-flash-player-mac-os.html 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 28.0.0.161

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

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. <Windows Only>

See if there are updates for your graphics drivers https://support.mozilla.org/en-US/kb/upgrade-graphics-drivers-use-hardware-acceleration

"...choose either Safe mode or Refresh"

If you hold down the <Shift> (Mac=Options) key when starting Firefox, this window pops up.

3) Chose "Refresh" & re-started FF

Refreshing Firefox {web link} is a LAST RESORT ! !

Refreshing Firefox -- easily fix most problems

If you're having problems with Firefox, refreshing it can help. The refresh feature fixes many issues by restoring Firefox to its factory default state while saving your essential information like bookmarks and open tabs. Everything else, like user settings and add-ons, are removed.

Well, THIS makes me feel a whole lot better about Tabs that are now "disappeared" and nowhere to be Found/Re-opened:

".. saving your essential information like bookmarks and open tabs

If, as stated, those "open tabs" have, in fact, been saved ... can anyone tell me where to Find & Re-Open them???

It should be in the History menu (Restore previous session), but you can also check this question.

'Restore previous session" is Greyed out in History ... N.G.

Finally opened Profile Manager, to find only one (1) Profile, marked "Default" ... so No Joy there either!

Do you have Old Firefox data folder on the Desktop?

You can check the sessionstore-backups folder top see if there are upgrade.js files available.

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Directory:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• http://kb.mozillazine.org/Profile_folder_-_Firefox

You will normally find these files in the sessionstore-backups folder:

• previous.jsonlz4 (cleanBackup: copy of sessionstore.jsonlz4 from previous session that was loaded successfully)
• recovery.jsonlz4 (latest version of sessionstore.jsonlz4 written during runtime)
• recovery.baklz4 (previous version of sessionstore.jsonlz4 written during runtime)
• upgrade.jsonlz4-<build_id> (backup created during an upgrade of Firefox)

You can copy a file from the sessionstore-backups folder to the main profile and rename the file to sessionstore.jsonlz4 to replace the current file (make sure to backup the current sessionstore.jsonlz4).

Firefox 56+ releases compress the files in the sessionstore-backups folder and sessionstore.jsonlz4 with LZ4 (.jsonlz4 instead of .js), so it is no longer easy to inspect them.

• https://www.jeffersonscher.com/res/scrounger.html

See also:

• http://www.ghacks.net/2014/06/27/mozilla-launches-improved-session-restore-firefox-33/