--- a/toolkit/components/extensions/ExtensionUtils.jsm
+++ b/toolkit/components/extensions/ExtensionUtils.jsm
@@ -360,21 +360,27 @@ class BaseContext {
    *
    * @param {Error|object} error
    * @returns {Error}
    */
   normalizeError(error) {
     if (error instanceof this.cloneScope.Error) {
       return error;
     }
-    if (!instanceOf(error, "Object")) {
+    let message;
+    if (instanceOf(error, "Object")) {
+      message = error.message;
+    } else if (typeof error == "object" &&
+        this.principal.subsumes(Cu.getObjectPrincipal(error))) {
+      message = error.message;
+    } else {
       Cu.reportError(error);
-      error = {message: "An unexpected error occurred"};
     }
-    return new this.cloneScope.Error(error.message);
+    message = message || "An unexpected error occurred";
+    return new this.cloneScope.Error(message);
   }
 
   /**
    * Sets the value of `.lastError` to `error`, calls the given
    * callback, and reports an error if the value has not been checked
    * when the callback returns.
    *
    * @param {object} error An object with a `message` property. May