i had this same problem with the same game too, also on a mac... what worked for me was adding a copy of the rom for pokemon emerald into the battery saves, and a copy into the save states folder as well. Then when in the game you can go to menu, and save like you normally would on a gameboy and it should work.
Here is a video showing what to do and how to do it if that couldn't explain it -
If you are playing multiple games I'm not sure if you can have a copy of each rom in the same battery save/save state folder... so i would create a sub folder for each game in which the game has its own battery save and save state, and in each of those is a copy of that specific games rom
i am currently doing this right now - it works