WebMail Notifier (for Gmail,Hotmail,Yahoo,AOL ...) 2.7.9
I use it for 3 yahoo mails, 1 gmail, facebook, ebay & twitter.
You don't need to check emails or facebooks for messeges or stastus updated.
It automatically test them & notify.
No need to login via site, you can straight away open it from addon, also you can open multiple mails at the same time. eg I open 3yahoo mails at the same time
Only thing to concern is if you use it on public computer others can log in to your account, but for personel computer great...
Notifier for gmail, yahoo, hotmail, aol and more webmails.
WebMail Notifier checks your webmail accounts and notifies the number of unread emails...
Supports : gmail, yahoo, hotmail, aol, daum, naver, nate, paran, POP3/IMAP and more
https://addons.mozilla.org/en-US/firefox/addon/webmail-notifier/
Facebook , eBay, Twitter... scripts can be found here
http://webmailnotifier.mozdev.org/scripts/