Build your first rule set

Limit the tool to your own device

A WebExtensions add-on is a browser package described in a manifest and, for many block lists, a JSON rules file. Build it for the profile you use. Do not publish it, do not ask others to install an unsigned copy, and do not point it at accounts you do not control.

This site does not ship an extension and cannot check yours. Follow the current developer notes from Mozilla for Firefox and from the Chromium project for Chromium-based browsers. Paths and flags change, so use those official notes for the load step.

List categories, not hopes

• Casino sites you have used in a browser.
• Sportsbook sites you have used in a browser.
• Affiliate landing pages that only exist to forward you onward.
• Leave banks, email, and work tools off the list.

Write the hosts on paper first. If you cannot name them without opening them, ask your support person to sit with you while you copy from history, then close history.

Write a small JSON rule

Use one block action so you can see whether the file loads. The host example.invalid is a placeholder. Swap it for a domain from your paper list, and keep resource types narrow until the test passes.

{
  "id": 1,
  "priority": 1,
  "action": { "type": "block" },
  "condition": {
    "urlFilter": "||example.invalid",
    "resourceTypes": ["main_frame"]
  }
}

Save that object inside the rules file your manifest names. Add further objects only after one block works. A huge first file hides a syntax error and delays the review you still need.

Load it in Firefox or Chromium

1. Confirm the manifest matches the extension format your browser documents now.
2. Load the folder as a temporary add-on in the developer screen.
3. Visit the placeholder only if you replaced it with a domain you mean to block.
4. If the page still opens, check JSON commas before you add domains.
5. Unload the add-on if you are experimenting on a shared family profile.

Stop after one successful block. Move leftover domains to the maintenance list instead of editing all night.

Keep permissions narrow

Request only the host and declarative blocking permissions the official notes require. Do not add remote code, an update URL you do not control, or a background task that phones home. A local blocker that needs an account has left the plan.

Store the folder where your backup already runs, and keep a copy of the paper list separate from the browser. Then schedule the first gap check on Maintain blocks.