"Edit" link missing in file preview for Microsoft Office documents

Summary

The "..." menu at the top right in the file preview that expands to show the "Edit" option for Microsoft Office documents when running Internet Explorer or Firefox doesn't show at all since Confluence 6.0.0-2016.06.

Steps to reproduce

1. Load up Confluence with Firefox or IE.
2. Embed a Word or Excel document in a page via Insert > File and Images.
3. Click on the thumbnail to open that document in the file preview.

Expected results

As well as the download, upload, share, and close icons at the top-right, there should be a "..." dropdown with "Edit" that allows the user to edit the document directly in Microsoft Office or OpenOffice (as per this page).

Actual results

The "..." dropdown is totally missing regardless of browser.