I made a really small modification to the template debugger. It makes it possible to enable the template debugger on a live store and only show it to admin so the other visitors won’t see it.
Edit: classes/templater/debug.tpl
Find:
{if isset($_smarty_debug_output) and $_smarty_debug_output eq "html"}
Add ABOVE:
{if $auth.user_id eq "1"}
At the very bottom of the file add:
{/if}
Save the file, upload, clear your cache and enable template debugging in the settings.
Now login at the store FRONT-END using your admin account. The template debugger should only popup when logged in to this account.
Try it out.