I have some suggestions for you:

Using Cookie Management Extensions: Check for browser extensions that offer advanced cookie management. They might provide selective cookie deletion options. Firefox has recommended this extension Cookie Quick Manager.

Using Separate Profiles: Create different browser profiles for different sessions. Each profile can have its own settings, cookies, and logins. You can understand it better here dedicated profiles .

Private Browsing: Use private browsing or incognito mode for sessions where you want cookies automatically deleted when closing tabs/windows.

Unfortunately, there is no built-in setting for this. You can keep all or clear all cookies, or you can manage them on a site-by-site basis. There isn't a feature to manage new vs. old cookies or retain only certain cookies per site. You can search for an add-on that has these feature, the closest one I saw in a quick search was:

Cookie AutoDelete:

When a tab closes, any cookies not being used are automatically deleted. Keep the ones you trust (forever/until restart) while deleting the rest.

I didn't study the description section closely, but it sounds like you may need to make a settings change so it works properly with third party (cross-site) cookies.

Thanks both.

Seems I already had Cookie quick manager installed but hadn't enabled it. I am going to have to do a bit of serious reading to get my head around all the settings.

Cookie Auto Delete just installed now. Likewise I am going to have to read a lot about how to use it.

I shall say I maybe didn't word the situation as good as I could have. Maybe because I don't fully understand the complete picture of how cookies work and interact with other tabs.

(Why can't I say both replies were helpful?)

(torn between posting here or making a new reply)

Looking in "Cookie Auto Delete" I have cookies from a local machine on my network. I understand that it is possible, but I am confused to how/why I have any. The site is a basic site that shouldn't send/use/need cookies. I'll delete them and see what happens. There is a log in required for ONE part of a page.... So it could be that.

Looking in "Cookie Auto Delete" I have cookies from a local machine on my network. I understand that it is possible, but I am confused to how/why I have any. The site is a basic site that shouldn't send/use/need cookies. I'll delete them and see what happens. There is a log in required for ONE part of a page.... So it could be that.

A lot of internal sites are built using Microsoft webservers which rely very heavily on cookies to maintain session continuity. Basically, if it doesn't get that cookie, you are just an anonymous somebody and not the person who was using the site 5 seconds ago.

I am trying to NOT be paranoid with how many cookies I get. But some just seem like leeches and I don't want to support them by having them remain in/on my machine once I've closed the tab.

I fear I am still too silly to know how to test that they are being deleted.

(subtle hint for help)

I'm guessing what I need to do is find a site that WILL give me cookies. Go to it, let them load, then close the tab and see if those cookies are then deleted.

That's the theory. Putting that into practice is a whole other can of worms.

Some cookies are just for the session so they would disappear when you close the tab. Other cookies are meant to endure.

The "Problem" is I have..... 39 WINDOWS open with Firefox.

Of that some have.... maybe 2 or 3 tabs.

SOME have a LOT. (at a guess 50+)

That is my "base line" of use. Places I visit a lot and often. Some have tabs left open for "articles" of interest. I know that is being anal and I could BOOKMARK them. I'm me.

Then now and then I go on trips to research things and go to shops and get all their cookies. I do close those tabs but it seems the cookies live on. Dunno why.

As said I shall have to sit down and try to understand the stuff from the cookie manager addons. But a while back I went through the cookies and there were cookies from shops I had been to a LONG TIME AGO and they were still there.

That annoys me - yes: shame on me for not dealing with them sooner - and so I am on this quest to ensure they do get wiped when I close their tab/s.