--- a/devtools/client/responsivedesign/resize-commands.js
+++ b/devtools/client/responsivedesign/resize-commands.js
@@ -54,20 +54,19 @@ exports.items = [
       },
       onChange: function (aTarget, aChangeHandler) {
         if (aTarget.tab) {
           ResponsiveUIManager.on("on", aChangeHandler);
           ResponsiveUIManager.on("off", aChangeHandler);
         }
       },
       offChange: function (aTarget, aChangeHandler) {
-        if (aTarget.tab) {
-          ResponsiveUIManager.off("on", aChangeHandler);
-          ResponsiveUIManager.off("off", aChangeHandler);
-        }
+        // Do not check for target.tab as it may already be null during destroy
+        ResponsiveUIManager.off("on", aChangeHandler);
+        ResponsiveUIManager.off("off", aChangeHandler);
       },
     },
     exec: gcli_cmd_resize
   },
   {
     item: "command",
     runAt: "client",
     name: "resize to",