Hey Roger,
I have written this b4 somewhere else....I have tried all browsers available, some give a good enough meter, some terribly choppy, some smooth but fast, etc.... I stick to Chrome and this is why: Flash is the trick.
http://www.wgt.com/forums/t/175545.aspx
As WGT runs on Flash any browser is affected by the Flash version installed. By de-activating the "latest" Flash version and using only the "second" flash version installed the meter behaves very nice, no matter how many windows you got open, programs running at the same time (not over doing it lol), downloading, etc.
As sometimes do not have my own stuff to play, I reach any other computer and install an older version of Flash & de-active the latest....it works great every time.
I suppose it works with any windows version, mac, or any other system, etc, again WGT runs with Flash and it is played now with many devices.
Must say, meter is smooth 99% of the time and I never get "metered" ever since I learned the trick, it is now like this for the last 2 years or so.
Good luck m8. Eric