--- a/browser/devtools/shared/widgets/VariablesView.jsm
+++ b/browser/devtools/shared/widgets/VariablesView.jsm
@@ -2043,17 +2043,17 @@ Scope.prototype = {
   /**
    * Gets top level variables view instance.
    * @return VariablesView
    */
   get _variablesView() this._topView || (this._topView = (function(self) {
     let parentView = self.ownerView;
     let topView;
 
-    while (topView = parentView.ownerView) {
+    while ((topView = parentView.ownerView)) {
       parentView = topView;
     }
     return parentView;
   })(this)),
 
   /**
    * Gets the parent node holding this scope.
    * @return nsIDOMNode