Yeah, it's not really great either. The about:memory page in Firefox is a little bit too technical compared with the about:memory in chrome that is, at least, simple and easy to understand what is going on.

In Firefox I still see a lot of memory commited to tabs that I've closed long ago, and can't really get a breakdown of my extensions memory usage.

Also what I was wishing is something more like a os task manager. Where I could kill or restart extensions that are using too much memory like I can do to normal applications.

Simply stating that this extensions is using too much memory so don't use it (a la IE) won't help. If that extension is the main reason I'm using your browser I'm not going to turn it off.

I'm not saying it would be easy or even doable right now, it's just what I wish to see in a future web browser to keep the memory down and prevent me from killing it and restarting it twice a day while working.