>If memory usage is so much higher than CPU usage, I have to wonder what it is that Mozilla is doing wrong with their architecture. Are they using pre-fork-style servers? Are they just provisioning poorly? What is it?

Or are they just serving up web pages to users? That's RAM and bandwidth heavy, but very CPU light. You still need the machines to scale your load, but you're not going to be using the CPU.

Realistically, for just about any application, you're going to be RAM-bound before you're CPU-bound. The exceptions are(off the top of my head) scientific computing and video rendering, both of which are CPU heavy, and are very deterministic in their behaviors, which allows for heavy optimization of L2 and L3 cache misses.