Rated 3 out of 5 stars

I like the idea. But can't figure out why this extensions shows '166Mb' while task manager says '190,000Kb' using Firefox 4b9pre

This review is for a previous version of the add-on (1.1). 

The add-on uses the Firefox memory service to get memory information. This is the same service used by about:memory, which indeed is less than what is displayed in task manager.