After changing the script, the new version is not automatically injected in already open tabs.

[Dook1]

To inject the modified script, have to reload open tabs.

[erosman]

That is the normal behaviour as it is not possible to remove the changes of a JavaScript that is already injected into a page and reinjecting the edited JavaScript can lead to unexpected behaviour.

Furthermore, FireMonkey users the browser API to inject and that API only injects JavaScript on new tab or refresh.

However, you can rerun a userScript from the toolbar popup.