ohh ok, you should look if there is a html code or a java code which you can implement in a html file and let it work in web viewer.
How you can work with a htlm file with java, taifun has on his page a tuturial for that.
Otherwise i see no possibility to use that.
MMaybe there is another way but i dont know it.
If you want a extension where people can log in with facebook than you hae to loof for facebook extension.