Rated 5 out of 5 stars

While you are waiting for FF4 compatibility, you might want to try Multifox which already works with FF4.

As much as I love CookieSwap, I believe Multifox is much better as it allows you to be logged into the same site twice (or more) simultaneously.

This review is for a previous version of the add-on (0.5.253).  This user has a previous review of this add-on.