I've lost my passwords of one or multiple accounts I have added to JD via Settings -> Account Manager - how to restore those?

You can't just copy your passwords out of JDownloader!
Please follow this guide:

1. If possible, try to get a new password via the "lost password" functionality of the website you've lost your password for.
2. Check if you are still logged in to that website via browser.
   Sometimes you can either view- or change your password in that active session.
3. Check if you've saved your login credentials in your browser and retrieve it from there: Chrome, Firefox, Opera (scroll down and search for "password manager")
4. Only do the following if you can't retrieve your password via any other way:
   Contact our support

We strongly recommend the usage of a password manager like for example KeePass (free and open source)!
This way you'll never lose any login credentials again!