Since I installed Gentoo its been bugging me that if I scrolled too quickly through a web page, it'd switch from “scrolling the page” to “next page” and flip to the page I'd used the back button to get away from. For a while I thought it was a Firefox thang, but I finally discovered that my mouse was giving different “button” messages depending how quickly I scrolled it. Normal, slow, scrolling was sending buttons “4” or “5” to the system, but quick scrolling sent buttons “6” or “7”.

A quick check of the xorg.conf file showed the mouse configuration looked like:

Section “InputDevice”
        Identifier  “Mouse0”
        Driver      “mouse”
        Option      “Protocol” “IMPS/2”
        Option      “Device” “/dev/input/mice”
        Option      “ZAxisMapping” “4 5 6 7”
EndSection

Reducing that ZAxisMapping option to just “4 5” seems to have cured things.