Drag and drop firefox tab on to firefox titlebar causes gray box to appear

This is still occurring and is worse than I thought. Dragging icons on the desktop also causes the big gray box to appear.
Is there a setting file that I could upload to see if anyone can replicate this problem?

Upon further investigation it looks like the problem is with the Window Rules plugin. If I enable this plugin, then restart the computer, the problem appears. I just have to drag an icon around on the desktop and I get the big gray bug. Disabling this plugin causes the problem to disappear immediately.
The only rules I have set up are various fixed window size rules.

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