Safari has shipped SharedArrayBuffer/Atomics support, but its usefulness for one of the primary use cases (games)
is limited by not being able to use it with WebGL. Firefox and Chrome both allow it.
For a real usage example, see https://statebuilder.com/ (a game I'm developing). It works on both Chrome and Firefox,
but I had to blacklist Safari due to missing WebGL with SAB support. Blacklist can be avoided by setting User-Agent to Chrome.
It is fixed in bug 223167 :)
*** This bug has been marked as a duplicate of bug 223167 ***