Comment by gsvelto

You're confusing general purpose locks with special-purpose ones used in the memory allocator. Firefox has its own GP locks, you can find them here: https://searchfox.org/mozilla-central/search?q=&path=xpcom%2...*

However those are not suitable for use in the memory allocator, and neither are WebKit's. WebKit uses os_unfair_lock within its memory allocator:

https://github.com/WebKit/WebKit/blob/520379e30f3b2b6d4de995...

And so does Chromium:

https://source.chromium.org/chromium/chromium/src/+/main:bas...