Visit about:debugging#/runtime/this-firefox in the address bar and search for the extension ID there.

Thanks that did it.

The extension is called Ghostery. Is there any way to limit the storage space in default/storage taken by a particular extension?

Bump.

You should contact Ghostery developer about their software and it's install issues here.

I seek a general solution for any potential extensions which suffer the same problem, something along the lines of a config setting perhaps. Ghostery is just the offender at this moment.

I have posted this second part of the problem (limiting storage use) in a separate question but a mod closed the thread considering it a duplicate of this question. If the mods will allow it I will mark this thread as solved and open a question in a new thread, also removing mention of Ghostery so it is clear I am looking for a generally applicable solution if necessary.

Internally Firefox is using the UUID to access the extension. Those UUIDs are stored in extensions.webextensions.uuids on the about:config page.

limit the storage space in cache2

The "cache2" folder (Cached Web Content) is completely different from the "storage" folder (Cookies and Site Data). The web cache is dynamic and volatile, you can clear it any time you want or even disable it entirely (browser.cache.disk.enable set to false in about:config).

Apologies I see the extension is saving its data in default/storage, not cache2. I have edited the post.

And yes, I have identified it already using its ID.

Ghostery only uses 5.2MB storage for me immediately after installing, uBlock Origin after many years uses 37MB.

I would uninstall Ghostery, refresh about:addons to clear storage, reinstall it and see if it still happens.

I can't find a way to do this for extensions generally but a bug report has been created by the Ghostery developers:

https://github.com/ghostery/ghostery-extension/issues/1256