Tried to change the default action to Windows Media. Did not help

Does anything happen at all? I think I remember seeing a bug about this, or something like it. SO tell me more. Perhaps I can remember.

Nothing happens even if you right-click the file and select open the file will not open. If I right-click and select "Save As", save the file locally then I can play it...

Using 91.5.1 I cannot duplicate the problem. It works.

The settings for attachments are in the handlers.json file in the profile folder. Try renaming the file, while TB is closed, and then restart TB and see if you can open attachments and set the opening app with the new handlers file. Help/More Troubleshooting, Profile Folder, Open Folder, to open the profile.

Rename handlers.json to handlers.bak; a new handlers.json will be created automatically on TB restart.

Did that did not work.

Uninstalled using Iobit Uninstaller - deletes everything

Reinstalled no Bueno (does not work)

PDF's open just fine

By the way, I am using Windows 11 Pro 21H2 64 bit upgraded from Windows 10

Check the Content-Type header in the source (Ctrl+U). For mov files, it should be video/quicktime. If it's not, it's not being properly encoded by the sender's mail app.

https://support.mozilla.org/en-US/questions/1366663

This is a Windows 11 computer, isn't Quicktime for a Mac? I use Thunderbird on other computers, they are Windows 10 and have no issue. Can you send me a MOV file so I can check it out. I used the Windows mail app and the file opens and plays. I am using VLC Player as my default audio video player (mp3 mp4).

The content type in Windows is video/quicktime for mov files, independent of the Quicktime app. What is the Content-Type for mov attachments on your system? Send yourself a sample mov from TB and view the Content-Type.

Attachment handling is partly broken in TB 91:

https://bugzilla.mozilla.org/show_bug.cgi?id=1747360

It's the "Movies and TV" app that is stock in Windows 11. I downloaded the video and it opens in the "Movies and TV" app just fine...

The MP4 MOV files seem to open ok it's just the MP3 files that do not open from the attachment in Thunderbird

I did a test with an mp3 attachment: sent it to myself, and checked the Content-Type header to see it was audio/mpeg. Right-click, Open, shows the dialog in the attached picture.

Mine does the same thing. The window opens asks how you want to open the file. I pick how I want to, open the file. Click "ok". The window closes and nothing happens... Doesn't matter if I pick another program to open the file. if I pick a different program to open the file same thing, the window closes the file does not open. If I choose to save the files saves then I can open the file.

In my example, the file does open in the selected app, but I can't explain why it doesn't in your case.

So now what do I do?

Attachment handling might be fixed in a future update, as in the bug mentioned above. Since I can't reproduce your issue, consider testing in a new profile: Help/More Troubleshooting, about:profiles. Your current profile would not be affected.

That worked when I created the new profile I can open the MP3 files. So should I just delete the original profile and use the other one from now on? Thanks for your help!

There is another profile don't know what it is used for maybe that is the issue. Here is a screenshot

A default-release profile is usually created during a failed update. You can Remove any unwanted profiles, as long as you don't need any data from them such as local mail or address books etc.