Firefox mostly pays attention to the Content-Type header sent by the server with the file; it doesn't pay a lot of attention to the file extension (e.g., docx).

The official content type should match up with "Microsoft Word Document" on the Options page. Do you see that listed there?

If a server doesn't send the official content type, you may need to manually associate the file. Do you see "Use other..." when you look at the listing in Options?

If not, set it back to "Always Ask." The next time you download a DOCX file, try the "Other..." option (example screenshot attached) to associate the content to Microsoft Word.

Does that work?

Whoops, just realized your question is about Thunderbird, so you probably don't have that same Download dialog. Is there a similar dialog?

I've done all of your suggestions. When I use Other, I don't get use MS Word Option just word pad which doesn't give proper formatting

George2018 said

I've done all of your suggestions. When I use Other, I don't get use MS Word Option just word pad which doesn't give proper formatting

From Other, do you get a "Browse" button which would let you go out to disk and find Word in the program files folder? For example (32-bit Office 2010):

C:\Program Files (x86)\Microsoft Office\Office14\WINWORD.EXE

jscher2000 said

George2018 said

I've done all of your suggestions. When I use Other, I don't get use MS Word Option just word pad which doesn't give proper formatting

From Other, do you get a "Browse" button which would let you go out to disk and find Word in the program files folder? For example (32-bit Office 2010):

C:\Program Files (x86)\Microsoft Office\Office14\WINWORD.EXE

No the other option doesn't give me MS word see the attached clips. By the way I'm using Office 2010

Can you add Word using the "Browse" button in the lower left corner:

Thank you ever so much. Funny how the simple solution always works. I never even noticed the browse at the bottom right corner..Duh! Thanks