Attach (recommended) or Link to PDF file here: https://www.recom-power.com/pdf/Powerline-AC-DC/RAC05-K.pdf

Configuration:
- Web browser and its version: Firefox 56.0 (64-bit)
- Operating system and its version: Windows 10 with OS Build 15063.632
- PDF.js version: ?
- Is an extension: Built-in

Steps to reproduce the problem:
1. Open Page

What is the expected behavior? To properly render the first page. 
![image](https://user-images.githubusercontent.com/1151969/31415345-b1504022-add7-11e7-855b-8030a308f7a2.png)

What went wrong? Renders poorly.
![image](https://user-images.githubusercontent.com/1151969/31415363-d8842096-add7-11e7-818d-728c1102891b.png)

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension): ?

}
      tmpCanvas = this.cachedCanvases.getCanvas(
        tmpCanvasId,
        newWidth,
        newHeight
      );
      tmpCtx = tmpCanvas.context;
      tmpCtx.clearRect(0, 0, newWidth, newHeight);
      tmpCtx.drawImage(
        img,
        0,
        0,
        paintWidth,
        paintHeight,
        0,
        0,
        newWidth,
        newHeight
      );
      img = tmpCanvas.canvas;
      paintWidth = newWidth;
      paintHeight = newHeight;
      tmpCanvasId = tmpCanvasId === "prescale1" ? "prescale2" : "prescale1";
    }
    return {
      img,
      paintWidth,
      paintHeight,
    };
  }