Better question here is, why is this not handled through the browser instead of relying on individual web apps to do it. Block third party cookies by default, delete other cookies on the last tab or window closed and prompt user to save cookies on a form submit ("do not delete cookies for this domain when leaving" type of prompt, for pages with logins, settings, etc). Also remove features that make easy fingerprintin…
We had P3P spec for it 20 years ago, even implemented in IE! And Google has been sending intentionally malformed P3P header to bypass it. Their trillion dollar business relies on users having difficulty stopping tracking.
(for amusement, google P3P and see what comes up first.)