Firefox also has to run its CI tests on all sorts of combinations of hardware and operating system: https://treeherder.mozilla.org/#/jobs?repo=mozilla-central

Firefox also has to run its CI tests on all sorts of combinations of hardware and operating system: https://treeherder.mozilla.org/#/jobs?repo=mozilla-central https://treeherder.mozilla.org/#/jobs?repo=mozilla-central By limiting to the newest OS, Microsoft can much more easily do quality control - of course, at the cost of shutting out many users.