3%-7% that use the button are most likely power users. It would be unwise to disenfranchise them as they are the ones who normally advocate your software to their friends (regular users).
That seems like it's the best option, actually. For power-users, a 3rd-party built extension is more likely to be updated / have the options you want than the button built into every version of the browser.
Sure, you could make an argument that 3%-7% is enough people to justify keeping the feature. Or you could make the argument that while it isn't enough, because they are the online non-shopping version of Alpha Consumers, it's worth keeping it to help get the browser promoted.
However you cannot argue that it has to be kept because every regular user wants this feature - statistics don't lie, clearly the majority of users don't care.
