Just a note Chrome has google sheets and it could be using that to open word doc as well. So did you try to run MS Word by itself to see if it really is there?

Chrome opens the docx files in MS Word, not in google sheets. It launches MS Word separately. I also for a fact know that MS Word is installed, functioning and bought on my computer.

If you have set Word as the default application in Windows to handle DOCX files then Firefox should select/present you with Word as the application if you download a DOCX file in the 'open with' dialog.

You can check the xulstore.json file in the profile folder for references about 'docx'.

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