In Firefox and at least the Firefox-fork LibreWolf you can specify which domains should be blocked by FF/LW. To achieve this, one needs to specify every single domain in the file policies.json using the following syntax (here some examples): "WebsiteFilter": { "Block": [ "*://*google.*/*", "*://*.twitter.com/*", "*://*.facebook.com/*", "*://*.gmail.com/*", "*://*.microsoft.com/*", "*://*.x.com/*", "*://*.office.com/*", "*://*.linkedin.com/*", "*://*.cloudfare.com/*", "*://*.telegram.org/*", "*://*.apple.com/*", "*://*.tiktok.com/*", "*://*.*.cn/*", "*://*.*.kp/*" ], If you make at least one single syntax error when defining here domain names in this array, then the respective domains do not get blocked by FF/LW. Here you can find the documentation about this kind of configuration (in section "WebsiteFilter"): https://mozilla.github.io/policy-templates/ How about giving users the chance to quite easily enter the names of domains they want to get blocked by Falkon within the Falkon GUI ?