Only rely on mousemove signaling end of drag in Firefox

Fixes #14, #19

Author: gaearon

src/HTML5Backend.js

@@ -177,16 +177,21 @@ export default class HTML5Backend {
     this.currentNativeHandle = this.registry.addSource(type, this.currentNativeSource);
     this.actions.beginDrag([this.currentNativeHandle]);
 
-    // If mousemove fires, the drag is over but browser failed to tell us.
-    window.addEventListener('mousemove', this.endDragNativeItem, true);
+    // On Firefox, if mousemove fires, the drag is over but browser failed to tell us.
+    // This is not true for other browsers.
+    if (isFirefox()) {
+      window.addEventListener('mousemove', this.endDragNativeItem, true);
+    }
   }
 
   endDragNativeItem() {
     if (!this.isDraggingNativeItem()) {
       return;
     }
 
-    window.removeEventListener('mousemove', this.endDragNativeItem, true);
+    if (isFirefox()) {
+      window.removeEventListener('mousemove', this.endDragNativeItem, true);
+    }
 
     this.actions.endDrag();
     this.registry.removeSource(this.currentNativeHandle);