A few people noticed that users submitted all kinds of URLs to Show Slow including those with file:// schema and even chrome:// schema (internal schema for Firefox extension files). Some users also sent URLs with private IPs and from localhost which can not be accessed from the internet by general public.
I added some code to handle these problems and now non-HTTP URLs are not going to be accepted and private network addresses will be ignored by default too.
You can still configure your own instance to accept private network URLs by tweaking the settings, but you probably shouldn’t remove localhosts anyway.
Don’t forget to run deleteignored.php to remove measurements for URLs that were not supposed to be tracked.