Why is gl.readPixels giving all 0 from Firefox?
===

I’m using WebGL to run some image processing (similar to Brad Larson’s [GPUImage](https://github.com/BradLarson/GPUImage) or the tutorial [WebGL Fundamentals](http://www.html5rocks.com/en/tutorials/webgl/webgl_fundamentals/)), followed by a CPU step that consumes the pixels. Unfortunately, when I call `gl.readPixels`, the buffer is all black in Firefox. Why?

Here’s a standalone example: http://jsfiddle.net/yonran/8C3n5/ In Chrome, the result is, “Within the framebuffer, there are 924 black pixels and 100 blue pixels,” while in Firefox, the result is, “Within the framebuffer, there are 1024 black pixels and 0 blue pixels.”

i thought this might be a synchronization problem, but adding `gl.finish()` or a `setTimeout` before reading doesn’t help. When searching, I found that multisampling can cause the framebuffer to be 0, but setting `antialias: false` within the `canvas.getContext` call doesn’t help.