--- a/toolkit/components/extensions/ExtensionPolicyService.cpp
+++ b/toolkit/components/extensions/ExtensionPolicyService.cpp
@@ -239,17 +239,19 @@ ExtensionPolicyService::CheckRequest(nsI
 // Checks a document, just after the document element has been inserted, for
 // matching content scripts or extension principals, and loads them if
 // necessary.
 void
 ExtensionPolicyService::CheckDocument(nsIDocument* aDocument)
 {
   nsCOMPtr<nsPIDOMWindowOuter> win = aDocument->GetWindow();
   if (win) {
-    CheckContentScripts(win.get(), false);
+    if (win->GetDocumentURI()) {
+      CheckContentScripts(win.get(), false);
+    }
 
     nsIPrincipal* principal = aDocument->NodePrincipal();
 
     nsAutoString addonId;
     Unused << principal->GetAddonId(addonId);
 
     RefPtr<WebExtensionPolicy> policy = GetByID(addonId);
     if (policy) {