[jefftk]

Firefox does not use WebKit (and at this point neither does anyone else), but they can look at patches to WebKit to understand how Apple improved Safari's performance. Because Apple produces the hardware, the OS, and the browser, the choices they make in the WebKit implementation are highly informative.

> it shows how being FOSS isn't enough

This is true for every app on iOS: even if you have the source code, you can't necessarily run a modified version, and so you're missing one of the main user freedoms that FOSS should guarantee. I wish Apple would rethink this, but Safari is still usefully open source.

[pjmlp]

No they cannot unless they want to contaminate their development, as far as I recall the licenses aren't compatible.

It is true for any commercial application with source code available since there are computers.

If the user freedoms were of any value as you mention, WebKit and Bink would use copyleft licenses.

[jefftk]

Just because you can't literally copy the code from one place to another doesn't mean you can't learn from it. I'm not a lawyer, but my understanding is it's fine to learn what series of system calls they're making and look at their optimizations.

[pjmlp]

Reading the code means analog copy paste.