Normally, when you choose Open instead of Save, Firefox will use the Windows Temp folder.

If you check the Downloads list, and "Open Containing Folder" for the Word document (you can use the icon on the right side), is it in the Temp folder?

If you launch it from there* can Word open it? If Word can open it there, it could be a problem in the hand-off from Firefox to Word. If Word can't open it, it could be a permissions issue with the file or folder.

* by double-clicking the file, or using right-click > Open

No, Word cannot open the files from the containing folder - I still get the same error message. However, if I right-click on the file I can open the file as a .pdf and view it - but with the volume of files that I need to look at, it would be totally impractical to have to do that with each and every file.

I do not think that it is a permissions issue because the computer next to mine can open the same files using Word - however that computer is still using Firefox version 24.

Oh... is the file actually a PDF internally but with a DOC or DOCX extension? No wonder Word is confused.

Does this problem occur with all DOC/DOCX files, or only particular sites? I recall that there was some Word DOC/PDF confusion with downloads from Dropbox. (Screen shot attached) However, I don't know whether that is relevant.

Could your Office viewer extension be a factor here or aren't you using that in this case?

No, the documents are uploaded as .doc or docx documents. I have to convert them to .pdf's if I want to view them... sorry about the confusion.

Everything says that the documents are Word files prior to me converting them to .pdf's.

Oh I see what you mean. So the document is valid to the PDF converter at least.

If you drag to move (or Ctrl+drag to copy) the document from the temp folder to another location, such as Documents or Desktop, will it open in Word from that location?

That's a great idea - I wish I would have thought to try that... but unfortunately, the documents won't open from my desktop either. I get the same error message...

In the download dialog, if instead of choosing Open you choose Save, will Word open the saved file? If so, we could try to compare the two to see whether we can figure out the difference.

No, the document will not open in Word if it is saved. The file is saved to my Downloads folder. When I try to open the file from there, I still get the same error message.

However, if I right-click on the file and choose 'Convert to Adobe PDF' from the drop-down box, the document will convert and open as a .pdf and I can see the file.

Is it possible that Firefox is mangling the extension, i.e., using DOC for files which should have DOCX, or vice versa? That's not as much of an issue for Word 2010 as it was for earlier versions, so might not be a factor.

Are any of the documents not confidential so you could send me one to examine? I'll send you a message through the board with an email address.

Yes, I can send you a copy - I will just remove any names...

But I will say that I am having the same problem with both .doc and docx documents (if the extensions that show are correct).

I am still having this problem - does anyone else have any suggestions? Thanks

To summarize our private email discussion for others taking an interest in this problem:

• The error occurs when using the Open option in the download dialog
  • Moving the file from the system Temp folder to a normal folder does not fix the problem file (Word still cannot open it)
  • The Adobe Acrobat converter can open the file even though Word can't

• The error does not occur when using the Save option in the download dialog and saving in a normal folder

• The solution in Microsoft's support article http://support.microsoft.com/kb/2749199 (bypassing protected mode for downloads) does not resolve the issue

Thank you for the summary  :)

I have solved the problem by rolling back to a previous version of Firefox. Thank you Jscher 2000 for all of your help  :)