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)



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      const m = this.ctx.mozCurrentTransform;
      const absDet = Math.abs(m[0] * m[3] - m[2] * m[1]);
      const sqNorm1 = m[0] ** 2 + m[2] ** 2;
      const sqNorm2 = m[1] ** 2 + m[3] ** 2;
      const pixelHeight = Math.sqrt(Math.max(sqNorm1, sqNorm2)) / absDet;
      if (sqNorm1 !== sqNorm2 && this._combinedScaleFactor * pixelHeight > 1) {
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        this._cachedGetSinglePixelWidth = -(
          this._combinedScaleFactor * pixelHeight
        );
      } else if (absDet > Number.EPSILON) {
        this._cachedGetSinglePixelWidth = pixelHeight;
      } else {
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        this._cachedGetSinglePixelWidth = 1;
      }
    }
    return this._cachedGetSinglePixelWidth;
  }
  getCanvasPosition(x, y) {