Really crazy errors appears if you add the following code in your overall_footer.html template:
<script>$(document).ready(function()

);</script>

I've checked this on 3.0 & 3.1 & firefox and you can't delete posts with javascript=on (mostly).
The message "Sorry but you can only delete your own posts." appears; or if you try your own posts "You cannot delete posts in this forum.".

Please try it as admin or moderator with delete permissions.

The bug could be this code which should be a trigger_error():
https://github.com/phpbb/phpbb/blob/3cb1907e76cc760f455f4571011bc4c517eb56db/phpBB/includes/functions.php#L2751

bug url: /posting.php?mode=delete&f=2&p=6