If you have more than one Gmail accounts (Yahoo mail or Hotmail accounts) and want to open them all at the same time in your Firefox browser are normally not possible. (You can do this in IE 8 without any add-on).

However, there is a very good add-on for Firefox browser called Multifox that allows you to connect to websites using different user names simultaneously.

After installation, this add-on will create a new menus ‘New Identity Profile’ in File menu. Just click on it open a new Firefox session.