Are your browsers up to date (FF10, IE9 can't support webGL anyway) ? Could you try also installing chrome ?
Are your graphic card drivers up to date ?
Also what is your operating system ?
Is the property "webgl" to on in the properties of your project ?
I have a less powerful config than yours, and I experienced nothing of the graphic tearing you're talking about.
Also consider posting a capx or an exported project for us to test.