redrum

Also, to block them in the firefox browser, you can also use the FoxyProxy extension, and use the proxy by patterns options to use a non-existant proxy for the domains that you want to block.

Edit to add config example:

You can use iptables to block connections, by example, using ufw the uncomplicated firewall:

# apt install ufw bind9-dnsutils  #  Install ufw and nslookup
# uIPs=$((nslookup reddit.com && \
  nslookup www.reddit.com && \
  nslookup redd.it && \
  nslookup redditstatic.com && \
  nslookup www.redditstatic.com) \
  | awk '/^Address: / { print $2 }' | sort -u); \
for uip in ${uIPs}; do \
  echo -n "${uip} " &&  \
  ufw deny from "${uip}" comment 'deny reddit.com'; \
  ufw deny out to "${uip}" from any comment 'deny reddit.com'; \
done;
# ufw enable
# ufw status numbered

You can also use a firewall to deny/reject outgoing and incoming traffic to those IPs. By example, with ufw:

# apt install ufw bind9-dnsutils  # install Uncomplicated Firewall and dig
# ufw enable  # activate the firewall
# dig +short reddit.com  # get reddit A IPs
151.101.65.140
151.101.1.140
151.101.193.140
151.101.129.140
# ufw deny in on all from 151.101.65.140 comment 'deny in connections to reddit'
# ufw deny out on all to 151.101.65.140 comment 'deny out connections to reddit'
. . . 

Or in only one line:

uIPs=$(dig +short reddit.com); for uip in "${uIPs}"; do echo "$uip"; done;

Debian has a list of vendors who sell it in a media (USB, DVD…), some of them also sell other distros.