You will need to install a user script manager extension to install this script.
Some forums based on DLE engine tend to hide direct link to anything behind redirect page and to do that they encode links as part of the URL to that page. So, when you want to copy a link you actually copy that redirect page link. Besides the fact that these links are obnoxiously long they are also completely unreadable and you never know where the link actually leads even from pop-up description since it also shows a link to a redirect page.
This script adds a mouseenter event to all links on all pages and if it looks like a link encoded by DLE then it decodes that link, replaces URL in a link with decoded one and detaches the event since normally there is no reason to check any link more than once.