It will take far less.

Once its share sufficiently drops, Google will pull out of their aggreement and Mozilla will collapse on itself. Unless Google is keeping them around for anti-monopoly purposes, in which case Firefox will just continue deteriorating in a zombie-like state.

> introduce Firefox Pro

If people aren't using the full feature browser today, why would they use it when it's not free?

Supposedely proposed changes would make it better and worth paying for.

Maybe user/developer support or some services ?

I disagree with the second point. Their email relay service and VPN is excellent.

Might be because it's not theirs. They are just resellers with a bit branding and some integration, at the moment.