[Jach]

Gentoo users like me fiddle with such things, they're just flags you can turn on before compiling. It's been a while since I experimented though, I didn't notice any advantage, with a disadvantage being an increase in compile time. I haven't tried on my newer machine yet though... but I suspect I wouldn't notice any difference.

[sfink]

In this case, it's not just a flag. Unless you're going through the Mozilla build system, in which case it kind of is. But what's actually happening is that it compiles the browser once, then runs it against some very small examples while collecting profiling data, then recompiles it while using the profiling data to guide optimization. That part about running the browser in the middle is what makes it complicated. (It can't do that when cross-compiling, for example.)