I'd love for the possibility to start paying for stuff again. Adds bore me. I wonder how much one would reasonably have to pay to make adds go away completely from Google and friends. It would also be in their interest to have customers pay a base fee as then It would be much easier for them to sell extended services like music, movies and privacy.
If you released a pay-for firefox then everyone would just start using iceweasel which could still happen if the ads get too annoying.
And thus we return to the glorious days of "shareware" and ad-supported "free trials".