I upgraded to 10.10 as it runs the magicmouse straight out the box, scrolling (including horizontal as well)

But it is a bit buggy.
I sometimes find that i need to click or double click a second time before I get the desired result. Furthermore when clicking between tabs in Firefox it closes the tab instead of switching to it.

Googling this problem I found this
Basically a magicmouse user is having the same problem with chrome.
It is suggested that sometimes when left clicking (for a right hander) you are actually middle clicking. This makes sense.
Now to solve it...Having tabs close down are truly annoying...