I sent a note to our internal lists today and already got a half dozen "I thought it was just my system..." responses, so for other people suffering in silence, and not recognizing this, I'll post it here too:
There's a bug in Xorg 6.9 (included in Nevada builds 28 & later, S10U2, and S10 patches) in which if you scroll the wheel too fast on your wheel mouse, you get left/right wheel events instead of up/down, which is particularly annoying in Firefox, which interprets left/right wheel as back/forward page history.
From recent conversation, it appears a lot more people have been suffering in silence with this bug than have reported it to us.
If you're one of those, you may not have noticed that bug 6372113 has been updated with both a fix-in-progress, based on the upstream fix from X.Org, and a simple workaround of:
Change or add this line in the "InputDevice" section for your mouse in /etc/X11/xorg.conf:Option "ZAxisMapping" "4 5 4 5"(The default ZAxisMapping in Xorg 6.9 is "4 5 6 7".)
With the workaround, Xorg will still think it's getting left/right events, but will report them to applications as simply more up/down events. This will break people actually using left/right capable devices, like the internal-frkit enabled Ferrari 3400 scroll pad/button/thingy. The actual fix will allow both types of scroll events to work correctly, and has been put into our sources for Nevada build 40.
Thanks for posting this !!