I use Chrome and pepperflash ... no problem with lags or glitches ... the only meter problem I have, is at certain times of the day (or some days entirely), the meter tends to drag and/or speed up with little warning. But I've had that same problem with different PC's, different browsers, and for the entire time that I've belonged to WGT.
Sometimes I can reboot my modem, change my IP addy in the process, and relog into WGT on a different server, and things work better. Some days, nothing works to make make the meter run a consistent speed, all the way down the scale.
It's a wonder that anyone that lives any distance from California can obtain a trouble free experience on WGT considering how many "hops" your requests take, and the "hops" the return data takes... in addition to server "glut" and local CPU performance ...