In-game Voice Chat Issue

I can’t seem to get my mic to work in-game. I hold down the assigned voice chat key but there is nothing. Just wondering if I need to reinstall the unity player or somehow modify its settings. If so, I’m wondering how I do that.

Currently using:

Firefox 23.0.1 on Windows 8 Professional 64-bit

Any help is much appreciated (:

My friend and I get this issue as well.
I’ve heard other people speaking to me, but I can’t seem to speak to anyone else, nor can my friend. I’d really like to know if there’s a way to fix it, or at least what’s going wrong (user error? hopefully?)