Works wonderful! Black list and white list for URLs can be used in a focussing period.
The add-on can distort the statistics of the focussing time. It doesn't check, if there was a cycle going on on the mobile when you finish in firefox.
So if you want to plant a tree between 1pm and 2pm, start the growing on phone and firefox at the same time you will get 2 trees and 2 hours of focussing which is kind of not whats really happens.
It would be awesome if sync would work down to a level, where I can start a cycle on my phone and the extension in firefox knows whats up and shows me the time and blocks what I want to be blocked.