BrokenLinkCheck - Free Broken Link Checker / Online Dead Link Checking Tool - find bad hyperlinks
Stylebot - Change the appearance of websites instantly. Preview and install styles created by other users on stylebot.me
Dead Link Checker - Check for broken links on any website
Dark Reader - Reduce eye strain in your browser with this extension that provides a dark theme for browsing.
LinkChecker - LinkChecker is a free, GPL licensed website validator.
Stylus - User Styles Manager - Stylus is a userstyles editor and manager based on the source code of Stylish version 1.5.2.