When a cookie is stored, it has an attribute of “domain”, which creates a restriction in which websites can subsequently access that cookie. For example, if you browse to example.org and it sends a response header with Set-Cookie: test=“somevalue”, then you browse to dodgysite.com, that site can not access the test cookie for the example.com domain.

You can press F12 and look at the network tab and then cookies, to see what cookies are sent and received in the http exchanges. You can look in the local data in your browser settings to find out what cookies are stored against a given site, but you can’t easily tell which cookies are used by a website because the browser will simply include all cookies for that site in every request.

A good start might be checking the storage.

Go to the website, right click on the page and choose Inspect, then in the panel that pops up look for the Storage tab.

On the left of this tab it has types of storage, and if you expand those you should see the different cookies and the domain they relate to.

I think Firefox might be blocking third party cookies by default for most sites now, but you will probably still come across some.

People, answer the question!!

There are extensions for that. But one universal way to do this is by opening the developer tools, either by hitting the F12 key like another commenter briefly mentioned, or thorough the application menu.

Then once the developer tools panel pops up, go to the Storage tab, select Cookies, and there you are. You’ll see a list of cookies grouped by the domain names they come from.