Nagger от Iris Dominguez

Nags you when you with a large red banner when visit specified sites. The banner is designed to discourage browsing, but won't truly block you from accessing the sites. The main idea is: if you can still go, you won't cheat by disabling the extension, but it will bother so you don't want to.

Some sites and keywords are enabled by default, but they can be easily disabled or modified from the configuration. The Add-on also supports a whitelist system, to avoid false positives from the keyword filtering.