Mozilla Firefox since 44 version (unlike 49 version of Google Chrome) supports push-notifications with payload. One can see examples here.
Firefox demo project, which is mentioned on Firefox wiki page, generates curl run parameters as:
curl -I -X POST --header "ttl: 60" "https://updates.push.services.mozilla.com/push/gAAAAABW4ccaidtFYOP2m56-XiY_NSKDXV1QiJ-4cpZG5BF-W7FjWE17SDt-h-b4b4VJamuvL30OcI9msyM1bupE9YHrwQZH4D7Uh2YS8cE_Tpvnvm3CgpBjblH58sE78HQjjbahB5NG4CkkKLj13gz0eB9mOAVGfcM3qo4Z61M5fn_6HZqLvCg="
Now how to add payload to curl, which will be delivered to registered service-worker?