The latest Firefox 3.5 nightlies now include Mibbit as a bundled IRC protocol web client so now, when clicking on an irc:// (or its encrypted variation, ircs://) link, it will be redirected to Mibbit so you can connect to the desired server using a web interface. Protocol web handlers support was introduced in Firefox 3
http://feedproxy.google.com/~r/MozillaLinks/~3/bqIS_XmG6j0/