Link to PDF file (or attach file here): [detect-form-fields.pdf](https://github.com/mozilla/pdf.js/files/287227/detect-form-fields.pdf)

Configuration:
- Web browser and its version: Firefox 46.0.1
- Operating system and its version: Ubuntu 16.04
- PDF.js version: 1.3.231
- Is an extension: No

Steps to reproduce the problem:
1. Open PDF
2. Look at entered text in form sections 8a and 9a

What is the expected behavior? Text is correct size:

![screenshot from 2016-05-27 12-32-04](https://cloud.githubusercontent.com/assets/33672/15619145/32ff065a-2407-11e6-8cfb-95905526fd91.png)

What went wrong? Text is very large:

![screenshot from 2016-05-27 12-30-58](https://cloud.githubusercontent.com/assets/33672/15619160/45016442-2407-11e6-85c0-faee9879c20d.png)

PdfBug console output:

```
11:56:13.291 PDF ef2293a3b9f4e0accbef97ee38798a2c [1.3 Mac OS X 10.11.1 Quartz PDFContext / Amgraf OneForm Designer Plus] (PDF.js: 1.3.231)1 viewer.js:6800:7
11:56:13.292 Warning: AcroForm/XFA is not supported1 viewer.js:6824:9
11:56:13.424 Warning: Unimplemented annotation type "FreeText", falling back to base annotation1 pdf.worker.js:9407:5
11:56:13.806 Warning: fontRes not available1 pdf.worker.js:9407:5 (logged 54 times)
11:56:13.898 Warning: Error during font loading: Font Helvetica-Bold is not available1 pdf.js:368:5
```

const style = element.style;
    style.fontSize = `${this.data.fontSize}px`;
    style.direction = this.data.fontDirection < 0 ? "rtl" : "ltr";
    if (!font) {
      return;
    }
    let bold = "normal";
    if (font.black) {
      bold = "900";
    } else if (font.bold) {
      bold = "bold";
    }
    style.fontWeight = bold;
    style.fontStyle = font.italic ? "italic" : "normal";
    
    const fontFamily = font.loadedName ? `"${font.loadedName}", ` : "";
    const fallbackName = font.fallbackName || "Helvetica, sans-serif";
    style.fontFamily = fontFamily + fallbackName;
  }
}
class CheckboxWidgetAnnotationElement extends WidgetAnnotationElement {