🧩 Firefox Browser Add Ons in a Kasm Container

This guide walks you through the process of installing the uBlock Origin extension in Firefox within a Kasm container. To build extensions like uBlock Origin into your Kasm container, you can use Firefox's ExtensionSettings policy. This policy allows you to configure and force-install specific extensions, ensuring the environment is pre-configured when the container starts.

📝 1. File Mapping

---

To get started, navigate to the workspace you would like to configure and choose "+ Add File Mapping":

📍 2. Set the Destination Path:

---

Within the Destination Path field, enter the following:

/etc/firefox/policies/policies.json

🔧 3. Configure the Policy

---

In the policies.json file, you will specify that the uBlock Origin extension should be force-installed. In the text field paste the following:

{
  "policies": {
    "ExtensionSettings": {
      "*": {
        "installation_mode": "blocked",
        "allowed_types": ["extension"]
      },
      "uBlock0@raymondhill.net": {
        "installation_mode": "force_installed",
        "install_url": "https://addons.mozilla.org/firefox/downloads/file/4261710/ublock_origin.xpi"
      }
    }
  }
}

✅ Outcome

---

The configuration should look like this:

Once the policies.json file is correctly configured, uBlock Origin will be automatically installed when Firefox starts in the container. The configuration ensures that the extension is active without requiring manual installation each time you launch the workspace in Kasm.