This is the simplest method which requires you to simply open about:preferences#privacy and manually go through each cookie via the "Cookie Manager" and ensure that it's placed into the correct container/context. Example:
Opening [https://www.facebook.com Facebook] in the personal container should place all the cookies in from FB into the "Personal"container is demonstrated by the screenshot below. Notice the "Container:Personal" at the bottom of the cookies properties.
[[File:FB Cookies Example.png|thumbnail|center]]