Just to be clear, not all restrictions need to be listed.
> Other properties should not have an effect on the marker box when declared directly on ::marker in the author or user origin of the cascade. UAs may either treat such properties as not applying, or enforce their value or inheritance from the originating element by setting a user-agent origin !important rule.
Firefox is basically doing something equivalent to the latter.
Bug 2009630 Comment 1 Edit History
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Just to be clear, not all restrictions need to be lifted.
> Other properties should not have an effect on the marker box when declared directly on ::marker in the author or user origin of the cascade. UAs may either treat such properties as not applying, or enforce their value or inheritance from the originating element by setting a user-agent origin !important rule.
Firefox is basically doing something equivalent to the latter.