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)

return !missingGlyphs[glyphId];
    }
    if (properties.composite) {
      const cidToGidMap = properties.cidToGidMap || [];
      const isCidToGidMapEmpty = cidToGidMap.length === 0;
      properties.cMap.forEach(function (charCode, cid) {
        if (cid > 0xffff) {
          throw new FormatError("Max size of CID is 65,535");
        }
        let glyphId = -1;
        if (isCidToGidMapEmpty) {
          glyphId = cid;
        } else if (cidToGidMap[cid] !== undefined) {