This severely underestimates the complexity of the Linux kernel.
Linux hasn't been a single person operation since the 90s.
In fact is the total comp of all the people significantly involved in Linux kernel development anywhere near the total comp of Mozilla's C-suite? I doubt it.
Most of us developers, devops and sysadmins are paid an obscene wage compared to many critical services like nursing. Is it fair? Probably not. But that doesn't have any baring on the complexity of Linux vs Firefox.
However, you can compare the people in the same business, such as those writing software for operating systems and web browsers and compare the cost and productivity in both.
Torvalds is at $2M and Baker is at $2.5M.
These comparions are caveman level arguments.