Some of our users are experiencing a problem using the mouse in Firefox, where the mouse appears to "float around" when you are drawing or moving items in Web Editor.
The reason for this is that in Firefox 49.0.2, asynchronous plugin rendering for Flash is now enabled by default. This causes problems with mouse tracking.
If you experience the problem, there is a patch to turn this behavior off.
The problem is described in the following bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1312528
To fix the problem, you will need to copy and paste this link in your Firefox browser address line: https://bugzilla.mozilla.org/attachment.cgi?id=8804461 and choose Install.
We hope that helps!