Julia Stiles has joined Mia Farrow in “Fran’s Bed,” the play written and directed by James Lapine that goes up Off Broadway at Playwrights Horizons later this summer.Heather Burns, Harris Yulin, Brenda Pressley and Marcia DeBonis have also been cast. Design team is Derek McLane (sets), Susan Hilferty (costumes), David Lander (lights), Fitz Patton (sound) and Elaine J. McCarthy (projections). Stiles’ stage credits include “Oleanna” in London last year and the Public Theater’s “Twelfth Night” in Central Park in 2002. Play begins previews Aug. 20, opens Sept. 25 and closes Oct. 9. Farrow also starred in the play’s world premiere at the Long Wharf Theater in 2003.