Update source file zen-preferences.ftl

Author: mr-cheffy

en-US/browser/browser/preferences/zen-preferences.ftl

@@ -69,6 +69,9 @@ zen-theme-marketplace-updates-success = Theme updated successfully
 zen-theme-marketplace-updates-fail = Couldn't find any updates!
 pane-zen-marketplace-title = Theme Store
 
+zen-look-and-feel-legacy-toolbar = 
+    .label = Use legacy toolbar position (Disclaimer: This feature is just for people who are used to the old toolbar position)
+
 zen-theme-marketplace-link = Visit Store
 
 pane-zen-CKS-title = Keyboard Shortcuts