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)

const newMap = Object.create(null);
  const toFontChar = [];
  let privateUseAreaIndex = 0;
  let nextAvailableFontCharCode = PRIVATE_USE_AREAS[privateUseAreaIndex][0];
  let privateUseOffetEnd = PRIVATE_USE_AREAS[privateUseAreaIndex][1];
  for (let originalCharCode in charCodeToGlyphId) {
    originalCharCode |= 0;
    let glyphId = charCodeToGlyphId[originalCharCode];
    
    
    if (!hasGlyph(glyphId)) {
      continue;
    }
    if (nextAvailableFontCharCode > privateUseOffetEnd) {
      privateUseAreaIndex++;