https://docs.rs/crate/quicksilver/0.4.0-alpha0.5 says:

If you want to test your application locally, use cargo web start --features stdweb and open your favorite browser to the port it provides.

However, that will just fail to build. The correct version should say:

If you want to test your application locally, use cargo web start --features quicksilver/stdweb and open your favorite browser to the port it provides.