Could you clarify your settings? I think you have:

Cookies

Keep until: Firefox is closed

With this setting, unless a site has individual permission to set persistent cookies, all new cookies should be set to expire at the end of the session.

There is a way to get those cookies back: restoring your previous session will resurrect the cookies for pages in the session history file. If you don't want Firefox to store session cookies in the session history file, you can change a setting:

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

(2) In the search box above the list, type or paste sess and pause while the list is filtered

(3) Double-click the browser.sessionstore.privacy_level preference to display a dialog where you can enter the desired value:

• 0 = save cookies/data for HTTP and HTTPS sites (default)
• 1 = save cookies/data for HTTP sites, but not HTTPS sites
• 2 = don't save cookies/data

That is precisely what I did... accept cookies and site data from websites and delete them when Firefox closes. Indeed, as you said " all new cookies should be set to expire at the end of the session." That is what makes sense BUT the cookies and site data do not get deleted when I close Firefox. I am not interested in getting cookies back ever, I just want them all gone from the last time I opened Firefox. Why would Firefox put such a straight forward setup in preferences and yet make it non functional?

That setting works for me, so I think it can work for you. If you open the Storage Inspector on a site (for example this one) -- using either

• "3-bar" menu button > Web Developer > Storage Inspector
• (menu bar) Tools > Web Developer > Storage Inspector
• (Windows) Shift+F9

-- and look at the cookies, what is the "Expires on" set to? Should be Session. Does that show correctly?

Use one of these to close Firefox if you are currently doing that by clicking the close X on the Firefox title bar.

• "3-bar" menu button -> Exit (Power button)
• Linux: File -> Quit
• Windows: File -> Exit
• Mac: Firefox -> Quit Firefox

If clearing cookies didn't help then It is possible that the cookies.sqlite file in the Firefox profile folder that stores the cookies got corrupted.

• rename/remove cookies.sqlite (cookies.sqlite.old) and if present delete cookies.sqlite-shm and cookies.sqlite-wal in the Firefox profile folder with Firefox closed in case cookies.sqlite got corrupted.

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Directory:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• http://kb.mozillazine.org/Profile_folder_-_Firefox