On it's own it's an incredible add-on, however if you take the further extensions into account it turns it into a serious 10/10.

The extensions that you can install, especially the core extensions maintained by piro themselves, makes it the main reason why I even use Firefox at all.

Using the multiple tabs handler, More Tree Commands, and the bookmark subpanel, makes researching topics a breeze. You don't have to struggle with the browser and can get on with your work.