another stupid mozilla-specific one liner

foo.js

// if you want to pin the popup open, from the browser toolbox:
gURLBar.popup.addEventListener('popuphiding', (e) => { e.preventDefault(); })

// to unpin it, close the window.
// if you need to get fancier, set a global bit of state and check it before
// preventing default, or, use a named function and call removeEventListener()
// when you're done.