Link above gives info on how to disable WebGL in Firefox and Chrome.
This link will describe in detail why you would want to do that.
Graphics Cards Face Internet-Borne Threats::Brought to you by TechWeb
WebGL Security Risks
added May 11, 2011 at 01:50 pm | updated May 16, 2011 at 10:20 am
US-CERT is aware of reports indicating that WebGL contains multiple significant security issues. The impact of these issues includes denial of service, and cross-domain attacks. WebGL is a new web standard that is enabled by default in Firefox 4 and Google Chrome and is included in Safari.
US-CERT encourages users and administrators to review the Context report and update their systems as necessary to help mitigate the risks.
Edited by buddy215, 16 May 2011 - 09:51 AM.