diff --git a/src/prefs.js b/src/prefs.js
index 2a1d7c7..5b45b03 100644
--- a/src/prefs.js
+++ b/src/prefs.js
@@ -14,3 +14,6 @@ pref('browser.search.suggest.enabled', false);
 
 // Empty new tab page: faster, less distractions
 pref('browser.newtabpage.enabled', false);
+
+// Allow UI customizations with userChrome.css and userContent.css
+pref('toolkit.legacyUserProfileCustomizations.stylesheets', true);