Firefox nuisance anyone.....

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maybe it's just an operator error here. I don't know. I just know it drives me nuts. When I scroll using the little bar thing-ama-jig over to the right, I will scroll down say, reading comments or what ever, when I use it to scroll back up, some how It closes my page every time. This is maddening. Places like MFP require that I log back in once the browser is closed. Does this happen to anyone else? How can I stop it?