You can disable the addon and re-enable it whenever you want using the standard add-ons/extensions feature of your web browser (but if you uninstall it, you’ll lose all your settings). Of course, you could lock your KeePass database to achieve a similar effect. Which is faster probably depends on how quickly you can enter your master password!
If you are interested in something less nuclear, follow in the thread Megamind linked to: How to configure the new Contextual Kee buttons