Attaching image using drag and drop leads to unpredictable position in FireFox 36

Bug Description

In Confluence release version 5.6.x, when user attach image through FireFox Confluence always positioned the attached image at the current cursor. In Confluence release version 5.7, it is not the case.

Some time Confluence will use the cursor and the other time it's positioned randomly.

How to replicate

Please refer to the attach screencasts on how to replicate the issue and the difference of behaviour compare with previous versions.