The OSS community has always had an uneasy tension between a) for-profit enterprise which provides most of the man-power and b) anti-commercial poor adolescents of all ages who simultaneously think that contributing to OSS is a moral obligation and that the license and copyright assignment they fetishize includes a "All contributors will be made happy despite their total lack of business sense" clause, somewhere.
Many core Python contributors including Guido are employed by companies like Google to work on it.
Mozilla is, technically, an exception: almost everyone is employed by the Mozilla corporation, a non-profit by virtue of its lucrative search deal with Google. Few projects have that luxury.
Something like 40% of Mozilla code is written by community contributors, which is quite remarkable. How many of those non-employees are paid by someone else specifically to work on Mozilla I don't know. i.e. I don't know if IBM pays people to work on Firefox they way they pay people to work on Linux.
1) To work full time on something like Linux, it really requires an external employer. So it isn't surprising that this is the case. To get involved does not, and certainly for a long time independent developers were as important as corporations there.
2) Everyone economically owns the output. I don't mean the copyrights. I mean everyone has a right to put the software to use for whatever purposes they want, whether in manufacturing, say, server appliances, or just running a web site (or even on my wife's laptop).
If the big companies stopped contributing to Linux tomorrow, would Linux die? I doubt it. So I suppose it depends on what you mean by "dependent." Certainly Linux is not dependent on corporate coding the way, say, Windows is.....
Yes, they do. Who do you think contributes to the Linux kernel everyday, only individual hackers all over the world pushing FL/OSS ? The vast majority of the contributors are big-tech-co affiliated who come from places like Red Hat, Intel, IBM, Novell, Oracle, AMD, Google, and more. Individuals and those not wishing to state their affiliation/place-of-work are only about 18% of the contributors to Linux.
Btw, this is part of the issue some people have with Ubuntu, in that it makes no contributions upstream to the kernel like Red Hat, Novell and others do. A Red Hat Greg DeKoenigsberg even said on OSNews once that "Canonical is a marketing organization masquerading as an engineering organization."[1]
Python's father Guido van Rossum and other core contributor are employed by Google and other big tech companies to work on Python.
Mozilla is mostly by Mozilla people, however it's basically alive because of the funding and ad deals it has with Google. Without that, it couldn't continue.