how to fix zawgyi font for gmail chat

When I use GMail Chat, I see ?? or rectangle box in Zawgyi Font. I already installed Zawgyi Font packeage. But it doesn't not resolve this issue.
Saturngod suggested as followed-
At FirFox Browser, type about:config in Browser Address bar, then search serif.x-unicode.
Put Zawgyi-one in front of default font.

1. Double-click on font.name.sans-serif.x-unicode and change - Zawgyi-one, Arial.
2. Double-click on font.name.serif.x-unicode and change - Zawgyi-one, Times New Roman.

In this way you see those web sites that don't not use Zawgyi in as default .