While glass mosaic itself is non porous and does not require sealing, the grout however is and may need to be sealed depending on where the mosaic has been laid. The cleaning process has therefore more to do with the grout than the glass mosaic itself.
Household cleaner, vinegar or anything acidic is fine for use over glass surfaces. A Scotch Brite pad can also be used on the glass, although nothing too dense like steel wool as this will remove the grout and is overkill. Generally a sponge with hot water and a little detergent is O.K. to remove grease (that the grout should be sealed if used as splashback behind cook tops).
Otherwise a wipe over with vinegar is fine. This can be 50% mix with water or straight but again be careful as the grout may change colour depending on what has been used.
It is always recommended that any cleaning agents be tested in an inconspicuous area first to see if there is any unwanted side effect.