"Then I opened Windows Task Manager and noted down the Memory consumption of all chrome.exe processes"
This approach won't yield an accurate result because of memory being shared between processes. As an example, 12 chrome processes might appear to be using 50mb each, but if half of that is from shared libraries, then the actual total is 325mb, not 600.
Is this surprising since chrome uses a sandbox model, It is firefox's apparent memory leaking that's the worry.
Chrome uses a process-per-tab model, so each tab you have open is its own running rendering engine/browser instance.
That is why you can have tabs crash and be closed without taking down the entire browser.
Firefox shares more state internally between tabs and as a result, a misbehaving tab can take the entire browser down.
All that being said, the Firefox team has been super aggressive as stomping out memory usage in the 6.0 and 7.0 releases and the work shows, they are doing a great job tuning Firefox.
Net-net, we all win.