Being prone imposes disadvantage on attacks, which makes sense for melee weapons and traditional bows. However, for things like crossbows and firearms, laying prone seems like it should have the opposite effect. The additional support and bracing received by laying on the ground would serve to stabilize one’s aim, and traditionally sharpshooters in militaries worldwide lay prone when making their long range shots.
Is this an unreasonable idea for balance purposes? Will anything break in my game if I house rule that characters receive advantage from being prone when firing a crossbow, rather than disadvantage?