drawingBufferWidth and drawingBufferHeight attributes
WebGL debugging and testing
Starting with Gecko 10.0 (Firefox 10.0 / Thunderbird 10.0 / SeaMonkey 2.7), there are two preferences available which let you control the capabilities of WebGL for testing purposes:
A Boolean property that, when true, enables a minimum capability mode. When in this mode, WebGL is configured to only support the bare minimum feature set and capabilities required by the WebGL specification. This lets you ensure that your WebGL code will work on any device or browser, regardless of their capabilities. This is false by default.
A Boolean property that, when true, disables all WebGL extensions. This is false by default.