Attachment preview spins in Mozilla Firefox

Summary

When selecting Preview next to a .docx or .pdf attachment that is listed in the Attachments Macro in Mozilla Firefox, the application spins and does not display a preview of the file.

Standard previews of .pdf and .docx also fail.

Environment

This has been tested in the most recent version of Firefox - 45.0.1

Steps to Reproduce

1. Open a page in Confluence that uses the Attachments Macro
2. Attach a .docx or a .pdf file to the page
3. Select the dropdown next to the new attachment
4. Click Preview

OR

1. Open a page in Confluence that has a .pdf or .docx file attatched
2. Click on the attachment to preview it

Expected Results

The file should pop up and be previewed within Confluence.

Actual Results

The preview module opens, but the page just spins. Below is a screenshot of what appears in the console:

Workaround

Open the page in Internet Explorer or Chrome.