I'm sure most of you use GMail at least as a secondary e-mail adress. Its simple and easy to use interface attracts many users. I'm sure a lot of people also use firefox too. Now from theese to advantages you can make a new one. Use GMail Notifier for firefox. Why? Because if you are interested in e-mails then your browser is already open, and now you can do other things easily without having to check your mail account every 5 mins if you are expecting an important mail. It supports checking for multiple accounts, you can set how often you want to check for new mails.Author's homepage: http://extensions.nexgenmedia.net
You can install it from here too: https://addons.mozilla.org/en-US/firefox/addon/173