Filed a #Firefox #bug report re: missing `counter-reset: list-item` in the default UA stylesheet. It only shows if you use the CSS property `all: unset`. Chromium-based browsers have `counter-reset` included.
See: https://bugzilla.mozilla.org/show_bug.cgi?id=1881517
Also see: https://github.com/elad2412/the-new-css-reset/issues/75