Think of it more as "we compile with -O3". If you installed with the .tar.bz2, you'd get that already. If you use a 3rd party produced .deb, they might build with -O2.
That's just an example; the blog is probably referring to PGO and/or LTO: profile-guided optimization and link time optimization, which require some fiddly setup that I believe third parties have traditionally not bothered with.
And yes, it's all open source. You can see all of the bits that go into producing that .tar.bz2. You can even see the full build log if you like, eg by going to https://treeherder.mozilla.org/jobs?repo=mozilla-release&sea... . Pick your platform, click on Bpgo, click on B, select the "log" link down in the lower left.
There are plenty of Mozilla-related things to complain about, openness of the browser development process is not one of them.
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.
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.)
That's just an example; the blog is probably referring to PGO and/or LTO: profile-guided optimization and link time optimization, which require some fiddly setup that I believe third parties have traditionally not bothered with.
And yes, it's all open source. You can see all of the bits that go into producing that .tar.bz2. You can even see the full build log if you like, eg by going to https://treeherder.mozilla.org/jobs?repo=mozilla-release&sea... . Pick your platform, click on Bpgo, click on B, select the "log" link down in the lower left.
There are plenty of Mozilla-related things to complain about, openness of the browser development process is not one of them.