Control: found -1 60.6.1esr-1~deb9u1 Just to clarify, this bug happens even on normal browser close, when session restore is *NOT USED* - that is, even when web pages are fully closed before quitting the browser.
And it happens even with setting "When Firefox starts" to "Show a blank page" (which should disable session restore functionality completely). So the option "Keep (cookies) until: I close Firefox" *never* does anything. It is quite deceptive :( As workarounds, only options not to retain cookies when closing firefox-esr browser I've found are: - installing add-on like "Cookie Autodelete" to remove cookies automatically on *tab* close - enabling "Always use private browsing mode" in "Preferences" / "Privacy & Security" (which also disabled sometimes useful session restore) - manually deleting cookies before closing browser. -- Opinions above are GNU-copylefted.