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)

this.running = false;
      this.cancelled = true;
      if (this.gfx) {
        this.gfx.endDrawing();
      }
      if (this._canvas) {
        canvasInRendering.delete(this._canvas);
      }
      this.callback(
        error ||
          new RenderingCancelledException(
            `Rendering cancelled, page ${this._pageIndex + 1}`,
            "canvas"
          )
      );
    }
    operatorListChanged() {