For Mac users, I prefer to use Kitematic UI to launch the container.
To do it manually, you can run it like this:
docker run -p 2525 -d gburton/mountebank-with-exposed-port:latest
Then you can look up the host port that is mapped to port 2525 of the docker container:
docker port <containerId> 2525
MAINTAINER Greg Burton firstname.lastname@example.org
RUN npm install -g mountebank --production