I think it is unrealistic to see Ad Block in Firefox because that is, after all, how Mozilla makes their money. People perform searches in the search bar and then when they click on an ad on the resulting Google search page Mozilla brings in a large portion of that revenue.
I think they really need to add more customization features for the tabs because that's why a lot of people use Firefox. They should have options to lock tabs, for example, so that they cannot be closed and such.
One other thing that I have been wanting to see is an easier way to customize toolbars. I should be able to place toolbars wherever I want, whether it be on the side of the screen or on the bottom. The same goes for the tab bar. I know that you can move individual buttons from one toolbar to another but I should be able to drag one toolbar next to another, much like how you can in Microsoft Office.