Edit in Office downloads the file when clicked from the Attachments macro

Summary

On Internet Explorer and Firefox, when you have the attachments macro in the body of the page and you click the Edit in Office button it downloads the file instead of opening it in Office.

Environment

Confluence Cloud. Tested on Windows 7 + IE11 and Firefox 51.0.1 (32-bit).

Steps to Reproduce

1. Add the Attachments macro to a page
2. Attach an Office file to this page (tested here with a xlsx file)
3. Click the Edit in Office button within the Attachments macro

Expected Results

The file opens in Office directly.

Actual Results

The dialog to download the file appears instead.

Workaround

Using Internet Explorer (or Edge) you can go to the page attachments list (Ellipsis menu > Attachments) and click the Edit in Office link from there and it should work.

Notes

Edit in Office has never been supported in Chrome (CONF-23322)