The ::-moz-range-progressCSSpseudo-element represents the portion of the "track" (the groove in which the indicator aka thumb slides) of an <input> of type="range", which corresponds to values lower than the value currently selected by the thumb.
The :-moz-full-screen-ancestorCSSpseudo-class applies to all ancestors of the full-screen element, except containing frames in parent documents, which are the full-screen element in their own documents. However, those elements' ancestors have this class applied to them.
The :-moz-loadingCSSpseudo-class matches elements, which can't be displayed, because they have not started loading, such as images that haven't started to arrive yet. Note that images that are in the process of loading are not matched by this pseudo-class.