I think this should stop my fireworks from damaging people

src/main/java/com/gmail/nossr50/listeners/EntityListener.java

@@ -148,6 +148,12 @@ public class EntityListener implements Listener {
         if (event.getEntity() instanceof ArmorStand) {
             return;
         }
+        
+        if (event.getDamager().hasMetadata(mcMMO.funfettiMetadataKey))
+        {
+            event.setCancelled(true);
+            return;
+        }
 
         double damage = event.getFinalDamage();
         Entity defender = event.getEntity();

src/main/java/com/gmail/nossr50/mcMMO.java

@@ -103,6 +103,7 @@ public class mcMMO extends JavaPlugin {
     public final static String blockMetadataKey    = "mcMMO: Piston Tracking";
     public final static String furnaceMetadataKey  = "mcMMO: Tracked Furnace";
     public final static String tntMetadataKey      = "mcMMO: Tracked TNT";
+    public final static String funfettiMetadataKey = "mcMMO: Funfetti";
     public final static String tntsafeMetadataKey  = "mcMMO: Safe TNT";
     public final static String customNameKey       = "mcMMO: Custom Name";
     public final static String customVisibleKey    = "mcMMO: Name Visibility";