Only macOS is supported right now. Web Replay's architecture should allow it to work on any operating system: the OS features needed are not specific to macOS or to POSIX systems. Still, porting it to other POSIX systems (Linux, Android) will be easier than Windows, due to the overlap with macOS. There is, however, a partial Windows port from an older version of the architecture that can replay a simple page but not rewind, which should make writing a complete Windows port easier.
From: https://developer.mozilla.org/en-US/docs/Mozilla/Projects/We...