Actually I think you are missing the point. The case that B is better than A should have been made by the devs already. I don't believe they have made their case for most of those removed features. The burden to show how these features are better is on them not. They are the ones making the claim that they are better.
As we all know by now the real reason for these changes are not because they are better but because they are different and more to the point because it is more like Chrome, the browser that the Firefox dev team has wet dreams about every night. This is just more of the same and the evasiveness about removing the tabs on bottom is typical of the Mozilla team.
I used to like Firefox because it was different from the other browsers and I liked those differences. and of course for the extensions and themes. The ones that the dev team keeps breaking many times permanently due to the insanity of the Rapid Release religion. The time is fast approaching that I may as well just install Chrome instead. Why settle for a bad copy when you can have the original? Seriously if they take away tabs on bottom and the ability to create sequential rows of tabs I will finally dump firefox for good.