Hm that's helpful. I know of a bug in my game where after you die if you leave it the sequence of meteors sometimes starts to build up and go super crazy after a while (maybe in XP that just happens all the time for whatever reason) -that isn't meant to happen! But during normal game it is fine. I built the game on my Win 7 64 pc with a Core 2 Quad QX9650 and Geforce 660 but I also tested it on a Win 8 PC with just a 2.66GHz Core 2 and a Radeon 4550 and it was a little slower but still ran ok.
The WebGL might be a red herring.
Could you confirm the lag and stuttering is occurring DURING the game itself or after death?
and what about in the chrome browser?
I don't have any access to Windows XP PC so if you have any time to test any of this for me it would really help me fix any problems.
I will also update the game and make all WebGL and particles optional.