Background: we (Gecko) have implemented the counter-set property, the built-in list-item counter for <ol>/<li> etc, and the ::marker pseudo for rendering. This all works fine, with one exception: counter-increment should be automatically set on list items, which means its value depends on the computed value of display. This means it's impossible to implement this in the UA sheet so we "adjust" the computed value in the style engine instead. At that point though, an author-specified counter-increment:none is lost if the initial value is none.

The natural solution to this problem is to change the initial value to something else, e.g. auto, which then computes to the relevant list-item counter value on list items and to none on other elements.

(A quick resolution would be most welcome since it blocks shipping this new implementation (which fixes a bunch of decades-old HTML list counter bugs in Gecko).)

CC @emilio @fantasai