[HarfBuzz] classic Mongolian shaping in Firefox

[tugi e]

Hallo Jonathan and Behdad,

After this change https://bugzilla.mozilla.org/show_bug.cgi?id=780409, Firefox shapes correctly the classic Mongolian. I think that is the first time that we could use classic Mongolian on Linux and Mac without any tricks. Thank you Behdad.

To use classic Mongolian shaping on Firefox, we have to set gfx.font_rendering.harfbuzz.scripts correctly. Is this possible to use Harfbuzz for Mongolian by default on all platforms except Windows, Jonathan?

Thanks
tugstugi