Whenever you click on mailto urls, the default email client is opened
up in Firefox.
You can change this default email client in Firefox by going to Tools--
>Options-->Applications.

Then scroll down the list by content type and find mailto. In the drop-
down menu to the right, select the mail application you want to use.

By default Hotmail or Livemail are not installed on Firefox and you
will have to add them by yourself.
The steps to add them can be found here:

http://www.dkszone.net/2009/06/how-t...vemail-as.html