Simply put, this extension works, nothing more. The regexes must be input one by one, and it pretends to offers a way to save the list: saving the add-on's Page... Which, of course, cannot be loaded, afterwards... So, yes, it works, but not in any practical sense, unless someone wants to block two or three addresses and nothing else. Other blockers have addressed it in a much easier way, by using a textarea, with each line being a regex, allowing copy/paste.

simple, straight forwards and it just works