Will I increase my security level by running Firefox from inside a Docker container (XUbuntu) under a non root user?
Does it make sense to do so to protect against different kind of malware & browser holes?
Why not? It depends of the use your are going to do. In that way if you dowload something for example, it's going to be downloaded inside the container. It will be accessible from the host only if you specify a volume mount during
docker run command. Doing that, any virus you download will be "sandboxed" inside the container.
But you must not forget that:
So could be a good a idea but is not a 100% free of risks technique. It depends of the use you are going to do.