Oh, and what I forgot is that you have to register an account on Hybrid-Analysis.com to get an API key. You can enter this API key in the extension settings so that the extension works.


Here's how to install a manually downloaded Thunderbird extension:

**1. Access Thunderbird's Add-on Manager:**

   * **Open Thunderbird:** Launch your Thunderbird application.
   * **Click the Application menu:** This is usually represented by three horizontal lines in the top-right corner.
   * **Navigate to Add-ons and Themes:**  You'll find this option in the menu that appears.

**2. Prepare for Installation:**

   * **Click the Gear/Settings icon:**  This is located in the top-right corner of the Add-ons Manager tab. 
   * **Select "Install Add-on From File..."**  A file browser window will open.

**3. Locate and Select the Extension:**

   * **Find the *.xpi file:** Navigate to the location where you saved the downloaded extension file.
   * **Select the file:** Click on the *.xpi file to select it.
   * **Click "Open":** This will start the installation process.

**4. Confirm Installation:**

   * **Review Permissions:** Thunderbird will display the permissions the extension requires. Carefully review these before proceeding.
   * **Click "Add" (or "Install"):**  Authorize the installation by clicking the appropriate button.

**5. Restart Thunderbird:**

   * **Restart Required:** You will likely be prompted to restart Thunderbird for the changes to take effect. 
   * **Click "Restart Now" (or manually restart):**  This will apply the installation.

**Troubleshooting:**

* **Compatibility:**  Ensure the extension you downloaded is compatible with your version of Thunderbird. Check the extension's description or website for compatibility information.
* **File Corruption:** If you encounter errors, try downloading the *.xpi file again in case the download was corrupted.

Let me know if you have any other questions!