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)



imgData,
    scaleX,
    skewX = 0,
    skewY = 0,
    scaleY,
    positions
  ) {
    if (!this.contentVisible) {
      return;
    }
    const ctx = this.ctx;
    ctx.save();
    const currentTransform = ctx.mozCurrentTransform;
    ctx.transform(scaleX, skewX, skewY, scaleY, 0, 0);
    const mask = this._createMaskCanvas(imgData);
    ctx.setTransform(1, 0, 0, 1, 0, 0);
    for (let i = 0, ii = positions.length; i < ii; i += 2) {
      const trans = Util.transform(currentTransform, [
        scaleX,
        skewX,
        skewY,