Firecracker launches small, but otherwise general purpose virtual machines. Containers, at least the standard implementations that most of us use, use kernel features like namespaces to isolate workloads, but still share a kernel so the sandboxing is not as strong.

Wasm is a virtual machine, just like for example the jvm is, that is designed around only allowing the executed program access to the host runtime via specific apis that are subject to security policies. It does not run arbitrary software, but rather only software built to target specifically wasm.

The software this post is about is just bundling a wasm runtime with other software for convenience.