Meeboo plugin for firefox

Your friends can see you online, even when you are checking email.
(I think, you have set it to visible in yahoo mail ...)

If you are using the firefox browser, get:
https://addons.mozilla.org/en-US/firefox/addon/5700

This will enable you to chat in to yahoo messenger and other such kinds.
Try it!

This will enable you to chat, however, more advanced features need to be added...