(Replay employee) Yeah, later in the post (https://medium.com/replay-io/effective-determinism-54cc91f56...) we mention needing mitigations to ensure that hashtable iteration is deterministic in cases where it affects how the browser interacts with the JS engine. There are others needed as well to ensure that the browser behaves the same across a large range of websites, my favorite is handling sites that sniff information about the system's math libraries by e.g. calling Math.sin() on specific values and testing the results --- the values when replaying need to be bitwise identical with what happened while recording.
Ah I shouldn't have stopped reading. Then as one of the rare browser replay experts (there's gotta be at least like... 7 of us right?) I can certify your project as the real deal.