When you're logged into at least one* account, you can do either of the following:
The way this list/roster is displayed can be controlled by choosing "Flat list" and "Show offline friends".
When checked, the option Show offline friends allows you to see what are all the usernames in your list, regardless of their offline status.
Choose Flat list if you want a simple display of names, without the groups from which the IDs are members of.
The two options shown above can be accessed either from Main Menu->Friends, or simply by right-clicking anywhere in the Friends list.
Facebook* doesn't allow you (at least for now) to organize the Friends list through a client. Or to chat with any other users that are not from the list it provides - in other words, you can only chat facebook-to-facebook.
The only option is to do it from Facebook site modifying your Friends lists or removing them:
Screenshots are from YateClient version 4.0.
* See here what features and limitations has Facebook chat, although it provides compatibility with XMPP clients, such as YateClient.
If you want to add/delete friends, organize your groups, you must do these changes logged onto Facebook site.