The 1858 Wright edition accidentally skipped the pronoun me here. The 1874 RLDS edition restored the me (probably by reference to the 1840 edition). We expect, of course, an object for the preposition before. For discussion of a similar case where a pronominal object was accidentally dropped after its preposition, see the discussion under 1 Nephi 7:20 regarding the apparent loss of me after against in the original manuscript.
Summary: Maintain the prepositional phrase before me in Mosiah 3:2.