Dallas, with a 4-16-4 (win-loss-tie) record, is MLS's worst team of 2003 and is experiencing its poorest season in club history. Assistant coach Colin Clarke will fill the head-coaching spot on an interim basis.
Jeffries, who leaves the Burn in the middle of his third season, finishes his Burn coaching career with a 23-36-16 record.
Clarke, who as a player represented Northern Ireland 38 times, was head coach of the A-League's San Diego Flash in 2000 before joining the Burn.