Usually firefox does not ship with it, but it's a one-click install when needed. It depends on the package though, some packagers build it with it bundled some

Usually firefox does not ship with it, but it's a one-click install when needed. It depends on the package though, some packagers build it with it bundled some don't. Since it's not a FOSS component it can't be bundled in FOSS distros though.