--- a/browser/base/content/browser.js
+++ b/browser/base/content/browser.js
@@ -900,17 +900,17 @@ function _loadURIWithFlags(browser, uri,
 
       if (postData) {
         postData = serializeInputStream(postData);
       }
 
       let loadParams = {
         uri,
         triggeringPrincipal: triggeringPrincipal
-          ? gSerializationHelper.serializePrincipal(triggeringPrincipal)
+          ? gSerializationHelper.serializeToString(triggeringPrincipal)
           : null,
         flags,
         referrer: referrer ? referrer.spec : null,
         referrerPolicy,
         postData
       }
 
       if (params.userContextId) {