Are you a webmail addict? 
Maybe you share a browser between family members, and you both use different webmail clients?  No matter the reason you need to use it – one thing is for sure.  This plugin is one of the best to make sure you stay up to date with your latest e-mails.
You can also use multiple accounts in a same host. The Web Mail Notifier currently supports:

mail.google.com(Gmail & Google Apps)
mail.yahoo.com (yahoo.com, ymail.com, rocketmail.com, yahoo.co.jp)
mail.live.com(hotmail.com, msn.com, live.com)
www.daum.net(hanmail)
www.naver.com
www.nate.com(nate.com, [...]

Always hate to see it, but you know it happens.  The good sites always go down first.  Sure, maybe they weren’t ready for all that traffic.  They had so much to live for though!  Need an extension to let you know when any web site is back up and running?  If so, it might be time to call Mr Uptime (who is now ready to use finally with Firefox 3).

This is an extension I mentioned here before.  It will [...]