When I check the Question Details > More System Details next to your post, I think I see the problem:

• Shockwave Flash 9.0 r45
• Shockwave Flash 21.0 r0

You need to get rid of the older Flash 9 plugin.

The official method is to do a full uninstall/reinstall of Flash. You can find a link to Adobe's uninstaller in this article: https://helpx.adobe.com/flash-player/kb/uninstall-flash-player-windows.html

But... it usually works to just physically remove the older file. To discover its location, type or paste about:plugins in the address bar and press Enter. You can use Find (Ctrl+f) for npswf to skip to the entries for Flash. Each should list the full path on disk.

On 32-bit Windows, the normal location is:

C:\Windows\System32\Macromed\Flash

If you go into that folder, be careful to delete ONLY the specific file listed in about:plugins because the others may be needed by other programs.

More likely, Flash 9 would be somewhere else on the system that the Adobe updater doesn't bother checking. If it is part of a program folder for a different program, it still is unsafe, but there might be another way to hide it from Firefox if you need that other program.

I could not find any reference to 9. Could it be called something else?

Hmm, try searching for shockwave flash in the about:plugins page.

The expected one is:

File: NPSWF32_21_0_0_213.dll

If you find another one, what is the Path listed?

The issue seems to be resolved. Thank you.