I really like this addon and use it for two use cases: 1. multi-account usage and 2. privacy protection
I don't need to explain the first point - that should be clear.
I have tested the 2nd point thoroughly and can confirm the following: It works.
- to lazy to write examples - so test it on your machine ;-)

I have used this for add-on for quite a number of years, have never experienced any problems, and appreciate the role that it plays (with the Facebook-container package as well). Lastly, as an add-on it's been vetted by Firefox, which should be another layer of correctness and security for the code.

Absolutely invaluable

Very powerful & useful addon.