Not to flog a dead horse here, but your argument is that without the extension people will try it a couple of times and then forget about you.com, and go back to default.
But your target demographic is here telling you that with the extension requirement, they will try it zero times, because they don't want to change their default to a service they haven't tried yet.
A better idea would be to unblock search, show results to everyone regardless of browser defaults, and push hard for the extension install on the search results page once people can see the value prop you're offering.
But your target demographic is here telling you that with the extension requirement, they will try it zero times, because they don't want to change their default to a service they haven't tried yet.
A better idea would be to unblock search, show results to everyone regardless of browser defaults, and push hard for the extension install on the search results page once people can see the value prop you're offering.