Viewer:  https://mozilla.github.io/pdf.js/web/viewer.html
Chrome on Windows 10
When the attached PDF file is viewed, some of the fonts display as garbled text. 
[Arial, Courier, Times New Roman]
The file views correctly in Adobe Reader.
[fff.pdf](https://github.com/mozilla/pdf.js/files/4652174/fff.pdf)

properties.fixedPitch = false;
    if (properties.builtInEncoding) {
      
      
      adjustToUnicode(properties, properties.builtInEncoding);
    }
    
    
    
    let glyphZeroId = 1;
    if (font instanceof CFFFont) {
      glyphZeroId = font.numGlyphs - 1;
    }
    const mapping = font.getGlyphMapping(properties);
    let newMapping = null;
    let newCharCodeToGlyphId = mapping;
    
    
    if (!properties.cssFontInfo) {
      newMapping = adjustMapping(
        mapping,
        font.hasGlyphId.bind(font),
        glyphZeroId
      );
      this.toFontChar = newMapping.toFontChar;
      newCharCodeToGlyphId = newMapping.charCodeToGlyphId;
    }
    const numGlyphs = font.numGlyphs;
    function getCharCodes(charCodeToGlyphId, glyphId) {