Gecko implements CSS lists as per spec, however no other browser does. This means that code like:

ol { counter-reset: none }

Does nothing on non-Gecko browsers, but break subsequent lists in Firefox because it overrides the UA sheet. See https://bugzilla.mozilla.org/show_bug.cgi?id=1765827 for the most recent example of this.

Maybe the list-item counter-reset should be magically auto-added to ol/ul/menu instead of via a UA sheet? That prevents authors from removing it but it might be needed for compatibility.