I was wondering if WebGL is considered stable enough to be enabled by default. It makes some PDFs render much faster and it has been off by default for a while now, so we have had quite some time to test it.

If we decide to enable WebGL by default, we should not forget to update https://github.com/mozilla/pdf.js/blob/master/extensions/chromium/preferences_schema.json#L39 as well.

/cc @yurydelendik 
/cc @Snuffleupagus (because IIRC you were testing WebGL too)

const scaleY = boundsHeight / height;
    const context = {
      coords,
      colors,
      offsetX: -offsetX,
      offsetY: -offsetY,
      scaleX: 1 / scaleX,
      scaleY: 1 / scaleY,
    };
    const paddedWidth = width + BORDER_SIZE * 2;
    const paddedHeight = height + BORDER_SIZE * 2;
    let canvas, tmpCanvas, i, ii;
    if (webGLContext.isEnabled) {
      canvas = webGLContext.drawFigures({
        width,
        height,
        backgroundColor,
        figures,
        context,
      });
      
      tmpCanvas = cachedCanvases.getCanvas(
        "mesh",
        paddedWidth,
        paddedHeight,
        false
      );
      tmpCanvas.context.drawImage(canvas, BORDER_SIZE, BORDER_SIZE);
      canvas = tmpCanvas.canvas;
    } else {