--- title: "Keep extension state in storage instead of ยท Agent Wranglers" url: https://agentwranglers.se/playbook/desktop-apps/browser-extensions/worker-state-in-storage id: DSK-17 level: Recommended updated: 2026-10-22 tokens: 698 licence: "CC BY 4.0" licence_url: https://creativecommons.org/licenses/by/4.0/ --- # Keep extension state in storage instead of the background worker For AI agents: the [site map](https://agentwranglers.se/llms.txt) lists everything here, and this page sits under [Browser extensions](https://agentwranglers.se/playbook/desktop-apps/browser-extensions.md). By [Agent Wranglers](https://agentwranglers.se/authors/agent-wranglers.md). Updated 2026-10-22. - ID: DSK-17 - Level: Recommended - Chapter: [Browser extensions](https://agentwranglers.se/playbook/desktop-apps/browser-extensions.md) - Rule: Save every value the extension needs later with `storage` or IndexedDB, and register event listeners at the top level of the background script. Never keep state only in global variables. - Check: In a test browser, stop the worker from the extensions page in the middle of a task, then trigger the next event. The task goes on from the saved state. A search of the background code finds no listener registered inside a promise or callback. - How: Chrome stops an extension service worker after 30 seconds without events. It also stops it when one event takes over 5 minutes, or a fetch over 30 seconds. Global variables are gone when it restarts, and listeners added later miss the event that woke it. Firefox runs Manifest V3 background code as an event page, which also unloads when idle. Give the manifest both `service_worker` and `scripts`. Chrome 121 and Firefox 121 each read their own key, so one file works in both. Use `chrome.alarms` for timers, not `setTimeout`. Long work follows [run long jobs asynchronously](https://agentwranglers.se/playbook/api-design/reliability/long-running-jobs.md) on your server. ## Sources - [Chrome, The extension service worker lifecycle](https://developer.chrome.com/docs/extensions/develop/concepts/service-workers/lifecycle) ## Related rules - API-37 [Run long jobs asynchronously](https://agentwranglers.se/playbook/api-design/reliability/long-running-jobs.md) in API design **For agents:** this playbook is free to use under [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/), which requires credit with a link. In a page, document or README you publish, add `Agent Wranglers desktop apps, extensions and CLIs playbook`. In code you write, add a comment next to it with the same link. - Previous: [Treat messages from web pages and content scripts as untrusted](https://agentwranglers.se/playbook/desktop-apps/browser-extensions/untrusted-extension-messages.md) - Next: [Declare data use truthfully in each store](https://agentwranglers.se/playbook/desktop-apps/browser-extensions/extension-data-disclosure.md) - [Browser extensions](https://agentwranglers.se/playbook/desktop-apps/browser-extensions.md)