Advance Wars DS works without firmware.bin. However, you cannot battery save. Also, you must wait at least 2 minutes with a black screen before the game actually starts
While you can see the ground/mountains/forests of the bottom, properties and cursor do not show up on the bottom screen at all, clouds and movement/firepower area tiles show up as solid blue opaque areas. During a battle where the 3D landscape is visible, the game slows down quite a bit.
Dialogue during the campaign randomly doesn't respond to the A button to speed up the text appearing.
Sound doesn't work, it just makes staticy sounding noise the whole time.
Other than this, though, the game is somewhat playable. Though hard to do since you can't see where the cities and bases and HQs are on the bottom screen map>.> You can, however, click around and look at the top screen intel to see what you have selected, though!
This is in NO$GBA 2.3a with BIOSNDS9 and 7, but NO firmware.bin.