Hi, sorry for replying late.
The extension will always get disabled if you add new permissions to the extension, or if you add new settings in the manifest.json file such as search engine, new tab URL, etc (I don't know the exact list of those settings).
It is tricky, as Chrome won't tell the user "there are new permissions to accept, do you accept?", instead it will silently disable the extension.
The recommended approach is to add optional_permissions instead of permissions when adding new features.
// Francois