There is a specific security issue with the WebGL implementation in Firefox 4.
Impact to users
This issue allows attackers to capture screen shots of private or confidential information.
Mozilla is aware of this bug and has issued a fix that will be released with the next version of Firefox, tentatively scheduled for June 21. This is a Firefox-specific implementation issue not a WebGL specification issue. In the interim, to protect themselves users can update to Firefox Beta or temporarily disable WebGL. To disable WebGL, in Firefox go to about:config and set webgl.disabled to true.
The bug was reported by Context.