How to load metabase's database backup inside Docker container?

When I first installed Metabase with Docker, I run the oneliner,

$ docker run -d -p 3000:3000 --name metabase metabase/metabase

Since then I’ve made a whole bunch of dashboards and questions…

I’ve made a backup like this,

$ docker exec -t metabase cat metabase.db.mv.db > /tmp/metabase.db.mv.db

So now, I have the backup in my machine. Now I try loading the backup setting the MB_DB_FILE env variable, but metabase creates a new H2 database…

$ docker run -d -p 3000:3000 -v /tmp:/tmp -e "MB_DB_FILE=/tmp/metabase.db.mv.db" --name metabase metabase/metabase

How could I load a backup database inside the Docker container?