@domubpkm I don't use the private browsing feature in Morph. But what I understand is it will delete not only all cookies, but your history as well. If you run Morph in regular mode with this script, you can keep the cookies with sites you trust and all your history, too.
Using this script would be similar to the Manage Exceptions feature in the Firefox Security and Privacy settings. There you can “Allow” certain websites to leave cookies while you have ticked a checkbox “Delete cookies when Firefox is closed”.
So, you can login quicker with sites you trust and also quickly find that page you visited a couple days ago in your history.