Disney’s “Mufasa: The Lion King” roared to the top of the U.K.-Ireland box office in its debut weekend with £4.4 million ($5.5 million), according to numbers from Comscore through Dec. 23.

Meanwhile, “Mufasa: The Lion King” will land in second place, having earned $13.3 million from 4,100 sites so far across the same time frame. In what some expected to be a more even box office ...