A header assembly for a movable partition includes an overhead track and a header pan. The header pan is configured to extend from the overhead track to an adjoining structure. The header pan, the overhead track, or a combination of both may form a fire-resistant barrier extending from a wall of the adjoining structure to an opposing wall of the adjoining structure. Movable partition systems may include header assemblies. Methods of forming header assemblies include positioning a header pan proximate to an overhead track and extending the header pan between a first wall and a second wall to at least substantially occlude a section of space therebetween. Methods of installing a movable partition include securing an overhead track to an overhead support structure, securing a retainer clip to an adjoining structure, extending a header pan from the overhead track to the retainer clip, and suspending a partition from the track.