While I definitely think Mozilla is great for the internet, their main product is terrible from a business perspective. Trying to monitize a piece of free software that you are selling on this privacy benifits is a loosing battle. The reason free software is free is _because_ it can sell more valuable ads by using your data. Products that you pay directly for don't need to worry about selling ads so they don't have to do tracking and such.
A paid browser at this point is realistically impossible to sell at any sort of scale because chrome is free. IMO Firefox Mozilla needs to make a new product that is paid. Someone on HN suggested email and/or other services that compete with Google's user product suite? At that point you are selling server space so its easier to get people to pay for it.