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): ?

const length = bytes.length;
  for (let i = 3; i < length; i += 4) {
    const alpha = bytes[i];
    if (alpha === 0) {
      bytes[i - 3] = r0;
      bytes[i - 2] = g0;
      bytes[i - 1] = b0;
    } else if (alpha < 255) {
      const alpha_ = 255 - alpha;
      bytes[i - 3] = (bytes[i - 3] * alpha + r0 * alpha_) >> 8;
      bytes[i - 2] = (bytes[i - 2] * alpha + g0 * alpha_) >> 8;
      bytes[i - 1] = (bytes[i - 1] * alpha + b0 * alpha_) >> 8;
    }
  }
}
function composeSMaskAlpha(maskData, layerData, transferMap) {