Webster (ankle) signed a contract with the 49ers on Wednesday.
With Richard Sherman (calf) on IR along with Ahkello Witherspoon (concussion) and Jason Verrett (hamstring) all dealing with injuries, the team elected to add Webster off Miami's practice squad. Webster played eight games for the Dolphins in his rookie season, averaging 19 defensive snaps per game while supplying 19 tackles and a pass breakup.