--- a/browser/components/touchbar/MacTouchBar.js
+++ b/browser/components/touchbar/MacTouchBar.js
@@ -227,26 +227,31 @@ class TouchBarHelper {
     // Remove unimplemented/mispelled inputs.
     prefArray = prefArray.filter(input =>
       Object.keys(kBuiltInInputs).includes(input));
     this._storedLayout = prefArray;
     return this._storedLayout;
   }
 
   getTouchBarInput(inputName) {
+    // inputName might be undefined if an input's context() returns undefined.
+    if (!inputName || !kBuiltInInputs.hasOwnProperty(inputName)) {
+      return null;
+    }
+
     if (typeof kBuiltInInputs[inputName].context == "function") {
       inputName = kBuiltInInputs[inputName].context();
     }
 
-    let inputData = kBuiltInInputs[inputName];
-
-    if (!inputData) {
+    if (!inputName || !kBuiltInInputs.hasOwnProperty(inputName)) {
       return null;
     }
 
+    let inputData = kBuiltInInputs[inputName];
+
     let item = new TouchBarInput(inputData);
 
     // Async l10n fills in the localized input labels after the initial load.
     this._l10n.formatValue(item.key).then((result) => {
       item.title = result;
       kBuiltInInputs[inputName].localTitle = result; // Cache result.
       // Checking this.window since this callback can fire after all windows are closed.
       if (this.window) {