Why does my mousewheel cause browser forward/back navigation, and how can I fix it?

Windows OS’s, Internet Explorer and Firefox both do this, a Microsoft optical mouse is attached via a ps port switchbox. Instead of scrolling the content window up and down, the mousewheel results in paging forward or back in the browser, which of course causes all sorts of frustrating events. I don’t see any relevant settings in Windows, IE, or Firefox. Looks like it may even happen on Macs. Also, why would anyone ever want or allow this to happen? Seems to me this is about the worst UI idea since putting the a System Reset button next to the Enter key.