A very recent Microsoft update has stopped Excel from being able to be downloaded/opened from web pages by default. 

It seems that the Excel update from Microsoft creates an auto default on a setting that prevents the data from being exported.   In order to allow the data to be exported, you need to follow these steps:

  1. Open an Excel sheet
  2. Navigate to File -> Options -> Trust Center -> Trust Center Settings -> Protected View
  3. Un-Check "Enable Protected View for file originating from the Internet"

Once you complete the above, try to open the Excel document again.

If this still does not fix the issue, try saving the document and then opening it.  Different browsers seem to have different results.

If you would like a more technical explanation, please read this article.