You don’t have to be a person who clicks on ads on parked pages to find it useful. These domains routinely come on other search engines and via typoquatting. Yes, even people like us mistype addresses and click on search results we otherwise think to be valid sites. At least I know I do!
As for people who don’t install extensions, I hope there will be other toolbars (and tools in general) for other platforms that reach these people. If you installed Firefox for your parents/grandparents, you could similarly install this add-on for them.
If you're using firefox, you're most likely completely aware that facebok!=facebook.