This comment doesn't even make sense, as with a little digging you could've found this[0] information yourself:
"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."
In fact, their documentation makes a specific call-out to TTT (Time-Travel Debugging) on Windows; so, I suspect that this is the API that they would like to use but are unable to do so at present (presumably because many of the features are still lacking in the API, which Microsoft could - and most probably would - enable).
"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."
In fact, their documentation makes a specific call-out to TTT (Time-Travel Debugging) on Windows; so, I suspect that this is the API that they would like to use but are unable to do so at present (presumably because many of the features are still lacking in the API, which Microsoft could - and most probably would - enable).
[0] - https://developer.mozilla.org/en-US/docs/Mozilla/Projects/We...