First, you need to assign a chat user name to your facebook account, you will not be using your email address for this. Go to your account settings and set it up. After you have done that you can create a jabber account on kopete. Use your new facebook username like this: firstname.lastname@example.org :
Then configure the connection setting to not use TLS and allow plain text authentication:
And last, do not forget to disable jingle support as it only works with gmail/gtalk accounts:
That's it, you now will be able to connect to facebook chat service from kopete and avoid opening a browser just for that.