I remember this statement, not from Chrome but from Fx defenders, back in the days. In fact it was Chrome people that belittled Fx due to its memory consumptions, I guess the tide is turned upside down now.
Firefox at workplace - it is the only option and whatever my mood is at home( IE, Fx or Chrome). They all perform nearly the same now. Mind you, I cannot differentiate differences in milliseconds. My gripe with Chrome is the faster it is the faster it crashes. Good thing it won't crash all the other tabs but reopenning pages that will eventually crash again pisses me off. IE 9/10 is the most stable based on my daily use.
The reason why Firefox received so much criticism was due to its poor performance and a memory leak that it had for years. Firefox's memory consumption on a cold start wasn't at all bad. But the problem became apparent the longer you left the browser open. Closing all the tabs back down to one would help a little bit, but it was endemic of a larger problem. Firefox at the time, and still does, keep all of its tabs as a single process. This is what helps drive memory usage down for Firefox. It also impacts the stability of Firefox too, as 1 tab can take down the whole browser.
If Firefox had low memory usage and great performance, you may have a point about Firefox. But clearly, you can see that low memory usage doesn't mean good performance. Before Chrome came around, you had Firefox or the aging IE6. Nobody cared about "speed" or optimization.
Firefox lags in my laptop when I open too many tabs but Chrome handles them smoothly. I think there is a reason why Chrome consumes more RAM than Firefox.
The reason is that Chrome has each tab as a separate process. Next time you have Chrome open, you will notice a bunch of "chrome.exe" in the task manager and only 1 "firefox.exe" regardless of the amount of tabs open.