Chrome has separate processes for each tab, as well as for each extension. In my Windows install I right now have only 3 tabs open, but it's using 24 processes.

Chrome has separate processes for each tab, as well as for each extension. In my Windows install I right now have only 3 tabs open, but it's using 24 processes. And in my experience, those processes all carry a goodly amount of overhead: even a simple page seems to consume 10s of MB, as does even a simple extension with no UI. I just created a HelloWorld page with nothing but that text, and it alone is consuming one process with 22.9MB. In contrast, Firefox pools those processes. I currently have 56 tabs open, but only 6 Firefox processes running, consuming a total of 1.7GB. So for example, there is (AIUI) just one single process that's responsible for all rendering behavior. I don't have the same detailed information about how much resources that HelloWorld page is taking, but it feels more efficient to me.