Do you have tabs open to web pages that use these cookies?

Firefox stores cookies used in tabs that are currently open in the sessionstore.js file as part of saved session data, so those cookies will be restored if Firefox is closed without first closing these tabs.

Only the initial tab is opened in my testing.

This still works for me.

Did you try to clear those cookies. "Remove Cookies" from sites causing problems:

• Firefox/Tools > Options > Privacy > "Use custom settings for history" > Cookies: "Show Cookies"

If clearing cookies didn't help then it is possible that the cookies.sqlite file that stores the cookies got corrupted.

• 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 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)
• http://kb.mozillazine.org/Profile_folder_-_Firefox

With Firefox closed, I deleted cookies.sqlite from the profile folder. Restarted Firefox and tested. It now deletes cookies on exit.

So you were correct, the cookies.sqlite file was corrupt and causing the behavior.

Thanks, no bug here, just a corrupted cookies.sqlite file!