Chrome consumes half as much CPU power as FF does, although both supposedly use hardware acceleration.
Chrome ships with its own Flash player version, which is optimized to work inside of chrome.
Beside that, Firefox has the problem that it is horrible slow (in every way), FF4 didn't made it any better. Thats really a shame because the project started as a better Netscape without being a blown up slow thing, no extensions, nothing fancy. Now it is like a modern Netscape.
About FF and JS, Firefox is more open to new JS features, they implement them already at their draft stage to let developer play with it (dunno if this is also the case for Jägermonkey), while Chrome (V8) and Safari (Nitro) just use the current standard without experimenting with it but trying to be as performant as possible.
