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)

baseFontCharCode,
            accentFontCharCode,
            accentOffset,
          };
        }
      }
      properties.seacMap = seacMap;
    }
    const unitsPerEm = 1 / (properties.fontMatrix || FONT_IDENTITY_MATRIX)[0];
    const builder = new OpenTypeFileBuilder("\x4F\x54\x54\x4F");
    
    builder.addTable("CFF ", font.data);
    
    builder.addTable("OS/2", createOS2Table(properties, newCharCodeToGlyphId));
    
    builder.addTable("cmap", createCmapTable(newCharCodeToGlyphId, numGlyphs));
    
    builder.addTable(
      "head",
      "\x00\x01\x00\x00" + 
        "\x00\x00\x10\x00" + 
        "\x00\x00\x00\x00" + 
        "\x5F\x0F\x3C\xF5" + 
        "\x00\x00" + 
        safeString16(unitsPerEm) + 
        "\x00\x00\x00\x00\x9e\x0b\x7e\x27" + 
        "\x00\x00\x00\x00\x9e\x0b\x7e\x27" + 
        "\x00\x00" + 
        safeString16(properties.descent) + 
        "\x0F\xFF" +