This is probably xulrunner's fault though, I suspect.
Do you have any actual data to support that claim (or suspicion, as you want)?
It's just a suspicion, as stated. The reason for this though is that Firefox has (or had) the exact same behavior in older versions I've used prior to switching to Conkeror.
I was thinking this was going to be your argument, which is why I pressed the issue. If you have a reproducible testcase where Firefox without plugins ends up "hogging system resources", then by all means report it.
I'd also prefer an Emacs-style keybinding set (or at least the ability to map one), so I don't have to switch muscle-memory mode when jumping from my editor to graphical browser. But, I'd be willing to give that up if the memory footprint of a thin Webkit-based browser is more minimal. I occasionally have to restart Conkeror after sustained heavy use due to it hogging system resources (it'll eventually bring my Atom n270 to a grinding halt). This is probably xulrunner's fault though, I suspect.