I am pretty sure that this graph is rendered to make IE7 look extra bad (I would actually guess that the green line would be Firefox 2 if I didn’t know the correct answer) – but we all know that opening new tabs in your browser is a memory killer for your computer. The good news is that the Firefox 3 team is working hard on making some significant improvements in the memory usage area as the graph from the tests above show you clear and loud.

Firefox 3 Memory Usage [blog.pavlov.net]