I'll point out that a Firefox OS app is, literally, a web app with a manifest file. If there's a web app out there that happens to work on Firefox OS, it's very close to being a Firefox OS app with ten minutes of effort to write the manifest file. You don't even have to put it on the store. Getting out of the walled gardens of the app world is a large part of the point of Firefox OS's goals.
Even if it didn't have any apps, it provides complete and open access to the Internet for $25 to people who might not otherwise have access to it. Wikipedia, email services, OpenStreetMap, Twitter, news sites, political forums, MOOCs. It's a chance to give the last billion people their voice on the open Internet.