Is it safe to delete Firefox website data?
Offline data, databases and local storage that websites and web apps stored in Firefox, in a folder for each site.
Usually safe
It can be recreated, but it takes a download, a reinstall or the tool's own command.
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What it is
Websites can store data in Firefox so they load faster and work offline, such as IndexedDB databases, service worker caches and local storage. Firefox keeps it in a folder for each site inside every profile, and a single site can store several gigabytes. On macOS 27, macOS protects Firefox's data folder so that other apps can't open or change it, so clear it from Firefox's settings.
If it's removed
You're signed out of the websites you clear, their saved preferences are reset, and web apps that work offline download their data again. Anything a web app saved only on this Mac, such as unsynced drafts, is lost.
What to do instead
In Firefox, choose Firefox > Settings > Privacy & Security, click Clear data for specific sites, and remove the sites you no longer use. To remove everything, click Clear browsing data and select Cookies and site data.
The free analyzer finds it and explains it, with these steps. The app doesn't remove it for you.
Sources
- support.mozilla.org/en-US/kb/clear-cookies-and-site-data-firefox
- cclsolutionsgroup.com/post/local-storage-and-session-storage-in-mozilla-firefox-part-1
- developer.mozilla.org/en-US/docs/Web/API/Storage_API/Storage_quotas_and_eviction_criteria
- wojciechregula.blog/post/golden-gate-appdata-protection
Last checked on 26 Sep 2026. Every entry is written and checked by hand; the app and the command-line tool use the same words.