Link to PDF file (or attach file here):
[pages4.pdf](https://github.com/mozilla/pdf.js/files/1128300/pages4.pdf)

Configuration:
- Web browser and its version: Firefox 54
- Operating system and its version: Win 10
- PDF.js version: 1.8.522
- Is an extension: no

What is the expected behavior? (add screenshot)
![chrome1-1 1](https://user-images.githubusercontent.com/146436/27918380-2f74512a-6245-11e7-8525-d0038fa6c2e8.jpg)
![chrome1-2 1](https://user-images.githubusercontent.com/146436/27918425-54f8e47e-6245-11e7-9bff-127f79ad0511.jpg)


What went wrong? (add screenshot)
![screenshot from 2017-07-06 12-10-30](https://user-images.githubusercontent.com/146436/27918442-5d57624e-6245-11e7-9436-5ba31cc8bd1a.png)
![screenshot from 2017-07-06 12-10-44](https://user-images.githubusercontent.com/146436/27918454-63b486da-6245-11e7-9eb5-c03aa5c40943.png)



_createMaskCanvas(img) {
    const ctx = this.ctx;
    const width = img.width,
      height = img.height;
    const fillColor = this.current.fillColor;
    const isPatternFill = this.current.patternFill;
    const maskCanvas = this.cachedCanvases.getCanvas(
      "maskCanvas",
      width,
      height
    );
    const maskCtx = maskCanvas.context;
    putBinaryImageMask(maskCtx, img);
    
    
    
    
    const objToCanvas = ctx.mozCurrentTransform;
    let maskToCanvas = Util.transform(objToCanvas, [
      1 / width,
      0,
      0,
      -1 / height,
      0,
      0,
    ]);
    maskToCanvas = Util.transform(maskToCanvas, [1, 0, 0, 1, 0, -height]);
    const cord1 = Util.applyTransform([0, 0], maskToCanvas);
    const cord2 = Util.applyTransform([width, height], maskToCanvas);
    const rect = Util.normalizeRect([cord1[0], cord1[1], cord2[0], cord2[1]]);