You're right, but most people will not notice Chrome's sluggishness because Google has worked very hard to ensure Chrome feels fast. That, and (in my experience) the fact that most Chrome users rarely go beyond 15-20 open tabs, make Chrome an overall better experience than Firefox for many people. In UX design, perception of speed counts almost as much as actual speed.
The key for that is that the UI is in a separate process.
Firefox for android (Nightly and Aurora) also do that.
Of course Chrome also has a process per tab (and in fact a few more than that), but the main thing is really a separate UI process (or lockless thread for that matter).
Interestingly this is also what made BeOS so snappy. All BeOS apps require an UI thread that is separated from the rest.
All that to say, while Firefox probably won't get a process per tab, I'd like if they ported the Android UI process to the Desktop.
