It sounds as though you are allowing Google to save a persistent cookie, and not clearing it between sessions. In that case, yes, Firefox will send the cookie to Google and the door will open...

Do you want to globally change your cookie settings to keep cookies only for the current session? You can do that in the Preferences dialog on the Privacy panel.

Edit menu > Preferences > Privacy

With the drop-down set to "Firefox will: Use custom settings for history"

Change "Keep until: they expire" to "Keep until: I close Firefox"

You may need to clear your Google cookies one time before this takes effect.

If you prefer to change your cookie lifetime setting only for Google, you can use the Permission Manager. Type or paste about:permissions in the address bar and press Enter. In the search box on the upper left side, type goog and pause while the list is filtered/rebuilt. Use the "Set Cookie" selector for google.com (and other servers if desired) to switch to Allow for Session.

You may also have to delete the sessionstore.js file in the profile folder.

You can use this button to go to the currently used Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)

It is possible that the cookies.sqlite file that stores the cookies is corrupted if clearing cookies doesn't work.

Rename (or delete) cookies.sqlite (cookies.sqlite.old) and delete other present cookies files like cookies.sqlite-journal in the Firefox profile folder in case the file cookies.sqlite got corrupted.

You can delete the permissions.sqlite file to reset all permissions.

Ah thanks for the useful replies. Now i realise what the problem is.

I use Google Multifactor authentication using Google Authenticator. Now in the old days (~ 6 months ago) Google used to tell you to not clear cookies if you selected the option "do not require authentication from this computer". Now i suspect Google does it automatically via Cookie settings in FF.

What this means is that now the Cookie Settings over-ride Firefox login and cache clearing. In the past it used to keep the Cookies (meaning i could avoid entering in 2nd factor authentication codes every time i logged into Google from the same computer) and also log me off when i closed FF. Now it doesn't log me out and i am logged in automatically. Kind of annoying.

about:permissions doesn't really give me the ability to preserve an option where it will log me out, whilst remembering not to ask me for authentication codes.

Hope this is clear. I really don't want to have to remember to log out every time i close FF. I know that's only a small extra step, but i usually forget. I guess i might have to hassle Google bout this one?

You can look at the CookieCuller extension.

• https://addons.mozilla.org/firefox/addon/cookieculler/

Cookies are only protected within the CookieCuller extension, so do not use "Clear Recent History", but let the cookies expire if you close Firefox and protect the ones that you wish to keep.