[Asraelite]

It's more complicated than that. You can use subtle differences in hardware and GPU rendering so that syscalls aren't even relevant. And you can never really prevent timing attacks, because you can just use a network request to get the current time from the server.

I've been wondering how hard it would be to make a completely fingerprint-proof browser.

One idea would be to run it in a deterministic emulator. All machine code instructions would be guaranteed to take exactly the same amount of time to execute on every machine, as far as is observable to the browser, and threads would be scheduled in the same order every time. Zero access to the host system through fonts, WebGL etc.

This would mean a massive performance penalty, but modern computers are fast enough that it might be usable for many sites. You could have a small number of discrete speed tiers, where you use the fastest tier that your computer is capable of.