Hello, this is an issue I have not come across before.
When viewing a pdf in Firefox 40, some characters (especially vowels and diacritic marks) in complex non latin scripts are not rendered correctly. To be specific, a glyph is often dropped for a default font. (The image shows the same pdf as seen with Firefox on the left, Preview on the right.)
From what I can gather, it is due to the OpenType Sanitiser as used by Firefox. What this does is validates a font for use in browser. It ensures that the rendering engine does not crash as a result of poor OpenType font files. But it appears to have higher standards than common desktop apps such as Adobe CS etc. It often rejects a glyph if it does not meet the standards during parsing. It even ignores specific tables, thus loosing Open Type features needed to display diacritics and vowel marks. Good for browser stability, bad for typography. If one value is deemed invalid dropping an entire table is over the top, especially where other apps seem to just get on with it and render the text correctly. There are an awful lot of ways a file can be fail.
What can be done to ensure font files are not rejected?
Why is Mozilla still using this library when no one else is?