--- a/devtools/client/application/panel.js
+++ b/devtools/client/application/panel.js
@@ -33,14 +33,12 @@ class ApplicationPanel {
     return this;
   }
 
   destroy() {
     this.panelWin.Application.destroy();
     this.panelWin = null;
     this.toolbox = null;
     this.emit("destroyed");
-
-    return this;
   }
 }
 
 exports.ApplicationPanel = ApplicationPanel;

--- a/devtools/client/dom/panel.js
+++ b/devtools/client/dom/panel.js
@@ -84,29 +84,25 @@ DomPanel.prototype = {
     };
 
     exportIntoContentScope(this.panelWin, provider, "DomProvider");
 
     this.shouldRefresh = true;
   },
 
   destroy() {
-    if (this._destroying) {
-      return this._destroying;
+    if (this._destroyed) {
+      return;
     }
+    this._destroyed = true;
 
-    this._destroying = new Promise(resolve => {
-      this.target.off("navigate", this.onTabNavigated);
-      this._toolbox.off("select", this.onPanelVisibilityChange);
+    this.target.off("navigate", this.onTabNavigated);
+    this._toolbox.off("select", this.onPanelVisibilityChange);
 
-      this.emit("destroyed");
-      resolve();
-    });
-
-    return this._destroying;
+    this.emit("destroyed");
   },
 
   // Events
 
   refresh: function() {
     // Do not refresh if the panel isn't visible.
     if (!this.isPanelVisible()) {
       return;