This addon modifies requests to http(s)://(www.)steamcommunity.com/?url=[some url here] and instantly redirects to the url instead of showing the linkfilter page. It's completely open source and hosted on GitHub.
Usage of this addon is at your own risk, don't use it if you are vulnerable to phishing attacks and use some common sense. After installing and/or enabling this addon there will be no notification at all about non-steam links (if the client pop-up has been disabled).