I tried adding my own endpoint, but the save button was still greyed out so it did not work. Maybe the feature is not fully implemented yet? In about:config, I could add the endpoint and api key, but not the model name.

Found the reason, HTTP-endpoints has to be localhost or 127.0.0.1, if you want to use other endpoints it needs to be HTTPS.

Keys that needs to be set in about:config

- browser.smartwindow.apiKey

- browser.smartwindow.customEndpoint

- browser.smartwindow.model

Adding my http endpoint (using LAN IP) seems to work, getting around the check in the regular settings.