Drag and Drop Attachments attaches multiple copies of a single attachment with Firefox 50.0

Summary

Using the drag and drop functionality to attach a file to a JIRA issue, multiple copies of that single attachment will get automatically attached to the issue.

Environment

JIRA 6.4.x
Firefox 50.0

Steps to Reproduce

1. Spin up or already possess a JIRA 6.4.x instance.
2. Open a Firefox 50.0 browser
3. Edit an issue in your JIRA instance
4. Drag and drop a file into the issue

Expected Results

A single attachment will be loaded into the issue.

Actual Results

Multiple copies of the same attachment are loaded into the issue.

Workaround

Option #1: Use another supported browser
Option #2: Upgrade JIRA to a 7.0.x or above
Option #3: Delete the additional copies of the attachment from the issue
Option #4: Use the manual upload method of adding attachments