I've abandoned tons of toy code but I have 1 thing I wrote in a weekend for myself that I've been mostly blindly using ever since. I just realized while typing this that it's been 8 years. It's a Firefox add-on that I only published to the "store" because running a local-only add-on is a PITA.

It takes regex(s), searches attribute values and/or inner text, and applies a given CSS rule to elements that match. The UI is awful (regex escaped to be inside a json string escaped to be inside a textarea all parsed by javascript) but I know how to use it.

It can probably be used for many things, but I just use it to set visibility: none on elements that link to sites I don't ever want to see (facebook, twitter, linkedin, popular pay/register-walled sites, etc). For example, my HN and reddit views just have blank lines where links any of those sites would normally be. For the most part, I add a site once, and forget they ever existed (except when their CEOs do awful things).