--- a/mobile/android/base/java/org/mozilla/gecko/prompts/Prompt.java
+++ b/mobile/android/base/java/org/mozilla/gecko/prompts/Prompt.java
@@ -541,11 +541,16 @@ public class Prompt implements OnClickLi
             try {
                 list[i] = items.getBoolean(i);
             } catch(Exception ex) { }
         }
         return list;
     }
 
     public interface PromptCallback {
+
+        /**
+         * Called when the Prompt has been completed (i.e. when the user has selected an item or action in the Prompt).
+         * This callback is run on the UI thread.
+         */
         public void onPromptFinished(String jsonResult);
     }
 }