"Almost all implementation work so far has been on macOS. Windows port work is underway, but is not yet working. The difficulties are in figuring out the set of system library APIs to intercept, in getting the memory management and dirty memory parts of the rewind infrastructure to work, and in handling the different graphics and IPC pathways on different platforms."
[0]: https://developer.mozilla.org/en-US/docs/Mozilla/Projects/We...
One of my favorite books starting out was the Stevens book about Unix. It only covers the differences in system call availability and behavior across Unix OSes. It doesn’t even touch graphics. It’s a big fat book just covering file, network, processes, and memory operations. No Mac, no Microsoft, just Unix.
https://en.m.wikipedia.org/wiki/Advanced_Programming_in_the_...
On Linux, Firefox has a bigger percentage (>30%), but (desktop) Linux is much less popular than macOS so in absolute terms they have the fewest users there.
51% Windows 10
27% Windows 7
6% Windows 8
6% macOS
11% Other (Linux, BSDs, etc)
https://data.firefox.com/dashboard/hardwareI think the Firefox Nightly, Developer Edition, and Beta channels have a slightly higher share of macOS and Linux users, but not much. There are a lot of Windows users out there; you just don't see them at JS conferences. :)
Replay requires a ton of difficult platform-level investment to get right and we're still actively finding bugs in the real world.
After it is validated, it will be easier to add the appropriate platform level bindings in other OSs.
Edit: to clarify, I refer to operating systems that have a considerable amount of potential and existing development, not systems with like 2 users .