Here you have to translate the URL, if it's relative, in order to open it. So, something like:
```js
let url = newURL || model.url;

if (url.startsWith('./')
   url = data.url(url.substr(2));

window.openWebPanel(model.title, url);
```

Important: you can't do that translation when you update the model, otherwise the user will get a different value than he set, it has to be here when the URL is passed to open the sidebar.