How to maintain different active sessions in single firefox and internet explorer?

The Multifox Firefox plugin may work for you: br.mozdev.org/multifox

firefox -p brings up a profile manager. you can use it to create multiple profiles. by running "firefox -p profilename -no-remote" you can open multiple profiles at once! therefore you can have as many logged in users in any site. don't know about internet explorer...

I use Yoono for Firefox this sort of thing.

It's designed to help out with your multiple social network accounts, but it works for any website.

After installing, you'll likely want to hide the toolbar Yoono adds (left side of the screen -> right click -> close), and then use the 'Yoono profile selector' (just left of the url) to add 3 gmail profiles, each with the same url: mail.google.com/

When you've added your profiles, you can open those profiles (with the 'Yoono profile selector') in different tabs, and enjoy browsing the same web site with different sessions in the same browser window.

The downside to Multifox Firefox, by the way, is you have to use a new window for each new session on the same web site.