Sorry, seems I wasn't notified of this review. The settings are linked to your browser. It prefers synced storage (tied to your Firefox account), but also uses local settings. If it forgets settings, that's likely a configuration issue on your end, and should also happen for other addons. If it's only Enhancer for Nebula, please open a new issue at https://github.com/cpiber/NebulaEnhance/issues/new with additional information
