I'm trying to create a docker container that will let me run firefox, so I can eventually use a jupyter notebook. Right now, although I have successfully installed firefox, I cannot get a window to open.

Following instructions from running-gui-apps-within-docker, I created an image (i.e. "sample") with Firefox and then tried to run it using

$ docker run -it --rm -e DISPLAY=$DISPLAY -v /tmp/.X11-unix:/tmp/.X11-unix --net=host sample

When I did so, I got the following error:

root@machine:~# firefox
No protocol specified
Unable to init server: Could not connect: Connection refused
Error: cannot open display: :1

Using man docker run to understand the flags, I was not able to find the --net flag, though I did see a --network flag. However, replacing --net with --network didn't change anything. How do I specify a protocol, that will let me create an image from whose containers I will be able to run firefox?

PS - For what it's worth, when I check the value of DISPLAY, I get the predictable:

~# echo $DISPLAY
:1

I have been running firefox inside docker for quite some time so this is possible. With regards to the security aspects I think the following is the relevant parts:

Building

The build needs to match up uid/gid values with the user that is running the container. I do this with UID and GID build args:

Dockerfile

...
FROM fedora:35 as runtime

ENV DISPLAY=:0

# uid and gid in container needs to match host owner of
# /tmp/.docker.xauth, so they must be passed as build arguments.
ARG UID
ARG GID

RUN \
       groupadd -g ${GID} firefox && \
       useradd --create-home --uid ${UID} --gid ${GID} --comment="Firefox User" firefox && \
       true
...

ENTRYPOINT [ "/entrypoint.sh" ]

Makefile

build:
        docker pull $$(awk '/^FROM/{print $$2}' Dockerfile | sort -u)
        docker build \
                -t $(USER)/firefox:latest \
                -t $(USER)/firefox:`date +%Y-%m-%d_%H-%M` \
                --build-arg UID=`id -u` \
                --build-arg GID=`id -g` \
                .

entrypoint.sh

#!/bin/sh

# Assumes you have run
#      pactl load-module module-native-protocol-tcp auth-ip-acl=127.0.0.1 auth-anonymous=1
# on the host system.
PULSE_SERVER=tcp:127.0.0.1:4713
export PULSE_SERVER

if [ "$1" = /bin/bash ]
then
        exec "$@"
fi

exec /usr/local/bin/su-exec firefox:firefox \
        /usr/bin/xterm \
                -geometry 160x15 \
                /usr/bin/firefox --no-remote "$@"

So I am running firefox as a dedicated non-root user, and I wrap it via xterm so that the container does not die if firefox accidentally exit or if you want to restart. It is a bit annoying having all these extra xterm windows, but I have not found any other way in preventing accidental loss of the .mozilla directory content (mapping out to a volume would prevent running multiple independent docker instances which I definitely want, and also from a privacy point of view not dragging along a long history is something I want. Whenever I do want to save something I make a copy of the .mozilla directory and save it on the host computer (and restore later in a new container)).

Running

run.sh

#!/bin/bash

export XSOCK=/tmp/.X11-unix
export XAUTH=/tmp/.docker.xauth

touch ${XAUTH}
xauth nlist ${DISPLAY} | sed -e 's/^..../ffff/' | uniq | xauth -f ${XAUTH} nmerge -

DISPLAY2=$(echo $DISPLAY | sed s/localhost//)
if [ $DISPLAY2 != $DISPLAY ]
then
        export DISPLAY=$DISPLAY2
        xauth nlist ${DISPLAY} | sed -e 's/^..../ffff/' | uniq | xauth -f ${XAUTH} nmerge -
fi

ARGS=$(echo $@ | sed 's/[^a-zA-Z0-9_.-]//g')

docker run -ti --rm \
        --user root \
        --name firefox-"$ARGS" \
        --network=host \
        --memory "16g" --shm-size "1g" \
        --mount "type=bind,target=/home/firefox/Downloads,src=$HOME/firefox_downloads" \
        -v ${XSOCK}:${XSOCK} \
        -v ${XAUTH}:${XAUTH} \
        -e XAUTHORITY=${XAUTH} \
        -e DISPLAY=${DISPLAY} \
        ${USER}/firefox "$@"

With this you can for instance run ./run.sh https://stackoverflow.com/ and get a container named firefox-httpsstackoverflow.com. If you then want to log into your bank completely isolated from all other firefox instances (protected by operating system process boundaries, not just some internal browser separation) you run ./run.sh https://yourbank.example.com/.