[ctde]

unfortunately this doesn't work if the user doesn't have write permissions for /etc/hosts already.

perhaps: echo "127.0.0.1 reddit.com # The real blackout" | sudo tee -a /etc/hosts ?

[LinuxBender]

If they are using the uBlock Origin addon they can go to Preferences -> My Filters and add:

    # Block Reddit Experiment
    ||redd.it^
    ||redditblog.com^
    ||reddit.com^
    ||redditinc.com^
    ||redditmail.com^
    ||redditmedia.com^
    ||redditstatic.com^
    ||redditstatus.com^

I've been using that as an experiment to see how many times I click a link that is blocked. Thus far only once.