Firefox support, issue #24.

File/data transfer works great, see chat.html.

Only slight issue is that multiple DCs are not finely configurable (JSON, utf-8, etc) due to lack of offer/answer exchange in Firefox. Options are to make an entire peer one configuration or to set a timeout to exchange such information before the new DC is created.

Also, the initial PC connection process is significantly slower than Chrome's. Could be just server latency but I noticed this locally when I first implemented this for Firefox as well.

@ericz, thoughts?