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)

height,
          true
        );
        this.compositeCtx = this.ctx;
        this.transparentCanvas = transparentCanvas.canvas;
        this.ctx = transparentCanvas.context;
        this.ctx.save();
        
        
        this.ctx.transform.apply(
          this.ctx,
          this.compositeCtx.mozCurrentTransform
        );
      }
      this.ctx.save();
      resetCtxToDefault(this.ctx);
      if (transform) {
        this.ctx.transform.apply(this.ctx, transform);
      }
      this.ctx.transform.apply(this.ctx, viewport.transform);
      this.baseTransform = this.ctx.mozCurrentTransform.slice();
      this._combinedScaleFactor = Math.hypot(
        this.baseTransform[0],
        this.baseTransform[2]
      );
      if (this.imageLayer) {
        this.imageLayer.beginLayout();
      }
    }
    executeOperatorList(