Can you include a screenshot

Screenshot is taking forever to upload due to crappy internet but here is the full name:

about.ef2a7dd5-93bc-417f-a698-a142c31168664fmozilla.com

It shows up on the "manage cookies and site data " tab.

Thanks for taking the time to reply.

I don't know how you are managing to see individual cookies in Settings. For more information, you could try the Inspector (ctl+shft+i), click on Storage in the menu across the top then Cookies and the site name (host) in the left panel.

You are right, it is not a cookie but the name of a website that is storing cookies on my computer.

I tried the procedure you suggested; inspector said there is no data present for selected host.

In any event, I am still mystified about the purpose of the cookies set by this site, why it/they suddenly appeared on my computer, and why I can't delete it/them.

You need to open the Inspector when you are on the site. While there, try clicking on the padlock icon at the left end of the address bar and then "Clear cookies and site data".

Probably you already tried to search any browsing history for that address, or even part of that address, such as ef2a7dd5. If not, you could paste a fragment of it to the address bar and pause for Firefox to generate matches. Or search in the History sidebar (Ctrl+H).

Assuming there's no history, maybe this is related to an add-on. Could you see whether you can find it here:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

More info on about:config: Configuration Editor for Firefox. The moderators would like us to remind you that changes made through this back door aren't fully supported and aren't guaranteed to continue working in the future. Since we are just doing a lookup, this is safe.

(2) In the search box in the page, type or paste uuid and pause while the list is filtered

Firefox should display two or three rows. If you see one with a huge amount of data, that's the one which could be interesting.

(3) Press Ctrl+F to open the Find bar and type or paste ef2a7dd5

If Firefox finds a match, it's probably like this:

"ef2a7dd5-93bc-417f-a698-a142c31168664f"

The part before that colon is the public ID of the add-on, in a more or less readable format. For example:

• "wikipedia@search.mozilla.org":"18f37a08-ba0f-42cd-a0a6-3486a1946366"
• "{faaf0e54-9c84-4a92-988f-389b4f613d28}":"d4c8bc96-56d1-4c92-b5f5-6abb047109e7"

Could you let us know what you find, if anything?

jscher2000:

Thanks, but there is no match for any part of the mystery string.

I didn't try to search my browsing history nor can I, as I delete it regularly.

Terry21:

Am I correct in assuming that when you say "the site," you mean the mystery site/cookies that I have enquired about?

If so, I cannot open inspector while on that site because Firefox claims it doesn't exist - or, more precisely, that it's having a problem finding it.

I appreciate your taking the time to respond, though.

OK, I'm far beyond my (modest) level of competence here, but I put just ef2a7dd5 in the Firefox address/search bar and got this site:

https://gitlab.torproject.org/tpo/applications/torbutton/-/issues/40017

with the cryptic (to me, anyway) message "Circuit UI does not display the right domain in reader mode. This may be related to tor-browser#40175."

That was exactly my first thought, too! Well, not really. I haven't had any interaction with Tor since a curiosity-driven look-see 10 or 15 years and about 5 laptops ago, so I can't understand why Firefox is now apparently planting Tor-related cookies on my machine.

There is a note in the source code that about.ef2a7dd5-93bc-417f-a698-142c3116864f.mozilla is used as a first party domain for about: pages (about: pages include the built-in Firefox Home / new tab page, the Settings page, and various other internal pages).

In bug 1300671, a comment says "If data: or about: url pages contain iframes pointing to some http/https site, those sites could of course do some tracking." Setting the first party domain of the cookie of the framed site to a value unique to about: pages prevents that cookie from being returned for that site in other contexts.

I can't think of where Firefox embeds a site into an about:page unless maybe it is related to searching for add-ons within the Add-ons page?

jscher2000:

I understood approximately none of this, but thanks for pursuing it. I resolved the problem by nuking Firefox and reinstalling it, although I had to hunt down and manually delete a number of mozilla directories as Windows uninstall alone was not sufficient to get rid of it.