I am using Mozilla as my default web browswer in Unix environment. It is great... except for a particular behavior of the browser window. When I middle click (MB2) the frame of the window, it doesn't go to the background, like all my other windows. Intead it opens a new tab (when I click at the top of the window). This is very annoying becaue I use MB2 /go to background all th etime. Any idea how to change that behavior and make it consistent with my general unix preference? Here is how it looks: see attachment.

Thanks in advance.