hide-em-ff by mgelsinger

hide-em hides content you don't want to see. You give it words or phrases, and it scans the pages you visit and hides anything containing them. Spoilers, a person you're tired of reading about, a topic you're trying to avoid, whatever it is, you decide what disappears.
Everything runs locally. Your list of terms is stored on your own machine and nothing is ever sent anywhere. There's no account, no sync server, no tracking. The extension only needs access to page content so it can do the hiding, and that's it.
Set up your terms once on the options page and hide-em works quietly in the background as you browse. Edit or remove them anytime.
Open source. The full code is on GitHub if you want to read exactly what it does before you trust it: github.com/mgelsinger/hide-em-ff