diff --git a/src/ZenThemesImporter.mjs b/src/ZenThemesImporter.mjs
index e9ebd50..a3f5a91 100644
--- a/src/ZenThemesImporter.mjs
+++ b/src/ZenThemesImporter.mjs
@@ -4,8 +4,13 @@ const kZenStylesheetThemeHeader = `
   * DO NOT EDIT THIS FILE DIRECTLY!
   * Your changes will be overwritten.
   * Instead, go to the preferences and edit the themes there.
-  */`;
+  */
+ 
+@-moz-document url-prefix("chrome:") {
+`;
 const kenStylesheetFooter = `
+
+}
 /* End of Zen Themes */
 `;
 var gZenStylesheetManager = {