Is there a Firefox add-on that will allow someone to easily open up a page in a new tab or window so it will not share cookies and other session information with other windows?

Basically, I want to be able to run Facebook, GMail, Google Search, etc, in separate sandboxes using different accounts.

I recall seeing a blog posting about an add-on that did this without forcing you to set up different Firefox profiles, but I can't remember where I saw it or what it was called.