Multiple attachment added when dragging file over the drop area in Firefox 50+

Problem

Multiple attachment added when dragging file over the drop area in Firefox 50+

Environment

 Only reproduces in Firefox since v 50, previous browsers are not affected.

Steps to reproduce

Captured as a video https://www.youtube.com/watch?v=Q-9XUT7P49Q 
Requirements - JIRA is up and running, has at leat 1 project.

1. Log-in into JIRA
2. Trigger Create issue dialog (Top button Create)
3. Open File viewer and drag the attachment over the drop area

Expected Result

Nothing happens, until drop action is finished

Actual Result

Attachments keeps being added, however the file is not yet dropped onto the drop area.

Notes

Issue occurs only for JIRA versions lower than 7.0.0

Workaround

New version of plugin was rolled out with a fix for older JIRA versions.

• 6.1-6.2: https://marketplace.atlassian.com/plugins/com.atlassian.jira.plugins.jira-dnd-attachment-plugin/versions#b156
• 6.3-6.4: https://marketplace.atlassian.com/plugins/com.atlassian.jira.plugins.jira-dnd-attachment-plugin/versions#b146

It's advised to upgrade to JIRA 7.0 or later.