Not always, but more frequently than never, I manage Firefox’s cookies by hand. Seeing what’s set, clearing out some I don’t like. Recently I discovered the button to do so in the Preferences dialog had disappeared from the Privacy tab.

Where did it go? It’s hiding under the history section. You have to change Firefox will: “Remember history” to “Use custom settings for history” and then the “Show Cookies...” button reappears. Because that totally makes sense. Just looking at cookies clearly requires that I also change to custom history settings.