Universal Pictures said Meryl Streep, Pierce Brosnan and Colin Firth are to appear at the upcoming London premiere of their movie musical “Mamma Mia!”. Based on the hit stage musical and featuring hits from the ABBA song catalog, the film version of “Mamma Mia!” is to open in the United States July 18. The world premiere of the wedding-themed movie is scheduled June 30 at London’s Odeon Leicester Square theater. Also slated to attend the event are supporting players Stellan Skarsgard, Julie Walters, Dominic Cooper, Amanda Seyfried and Christine Baranski, the movie studio said.