I don't think this is a new feature... Typically, cookies persist as long as the server wants them to unless: '''(1)''' Firefox Privacy options for cookie lifetime is set to "Keep until: I close Firefox" (and there isn't an exception for the particular site) To check on that: "3-bar" menu button (or Tools menu) > Options In the left column, click Privacy. Then on the right, if the selector is set to "Firefox will: Remember history" you can change that to "Firefox will: Use custom settings for history" to view detailed settings. '''(2)''' Firefox Privacy options have "Clear history when I close Firefox" and the Settings dialog has a checkmark for cookies '''(3)''' An extension that manages cookies clears them '''(4)''' An external program cleans Firefox data '''(5)''' Your cookies.sqlite database file becomes locked or corrupted Regarding that last one, you could remove the file (effectively clearing all cookies) and have Firefox create a fresh one. If you want to try that: Open your current Firefox settings (AKA Firefox profile) folder using either * "3-bar" menu button > "?" button > Troubleshooting Information * (menu bar) Help > Troubleshooting Information * type or paste about:support in the address bar and press Enter In the first table on the page, click the "Show Folder" button. This should launch a new window listing various files and folders in Windows Explorer. Leaving that window open, switch back to Firefox and Exit, either: * "3-bar" menu button > "power" button * (menu bar) File > Exit Pause while Firefox finishes its cleanup, then rename '''cookies.sqlite''' to something like cookies-old.sqlite. If you see a file named localstore.rdf, rename that one to localstore.old. If you see other similarly named files like cookies.sqlite-shm and/or cookies.sqlite-wal, you can delete those. Start Firefox back up again. Can it remember persist cookies now?