Intentional YT stores all extension data locally in Firefox using browser.storage.local.

What the extension stores:
Settings you configure in the popup, including Night Lock times, entertainment limits, browsing-mode state, research mode state, current topic keywords, and trusted channel names.
Local usage state needed to enforce the extension rules, including current watch timer values, daily usage totals, browsing cooldown state, and the active block reason.

What the extension accesses:
YouTube page content on youtube.com and www.youtube.com so it can hide recommendation surfaces, detect navigation changes, and show overlays.
Tab information needed to detect active YouTube tabs and redirect blocked tabs to the extension's own blocked page.

What the extension does not do:
It does not send your data to any remote server.
It does not use analytics, telemetry, advertising, or third-party tracking.
It does not authenticate users or sync data to a cloud service.

Data sharing:
All data remains local to the browser profile where the extension is installed unless Firefox itself syncs extension storage as part of a separate Firefox Sync feature you have enabled.

Data retention and deletion:
Stored settings and usage values remain in local extension storage until you change them, reset them, or remove the extension.
Removing the extension removes its local extension storage according to Firefox's extension uninstall behavior.