Update firefox image

- Add example usage in such a way that `DIR=firefox make run` work
- Use bullseye (stable) instead of sid (unstable) as base-image
- Make it possible to change this at buildtime with the buildarg DEBVERSION
- Take firefox from bionic (newest LTS) instead of xenial (older LTS)
- Make it possible to change this at buildtime with the buildarg UBUVERSION
- Use UTF-8 as default LANG
- Run it as user "user" with homedir "/home/user"
- Make it possible to change this at buildtime with the buildargs USER and HOME

firefox/Dockerfile

@@ -1,12 +1,24 @@
-FROM debian:sid-slim
+#Run firefox in a container:
+#
+#docker run -d --rm --net host \
+#	--device /dev/snd --device /dev/dri -v /dev/shm:/dev/shm \
+#	-v /tmp/.X11-unix:/tmp/.X11-unix -e DISPLAY=unix$DISPLAY \
+#	-v $HOME/Downloads:/home/user/Downloads \
+#	-v $HOME/.mozilla:/home/user/.mozilla \
+#	--name firefox jess/firefox
+#
+
+ARG DEBVERSION=bullseye-slim
+FROM debian:$DEBVERSION
 LABEL maintainer "Jessie Frazelle <jess@linux.com>"
 
+ARG UBUVERSION=bionic
 RUN apt-get update && apt-get install -y \
 	dirmngr \
 	gnupg \
 	--no-install-recommends \
 	&& apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 0AB215679C571D1C8325275B9BDB3D89CE49EC21 \
-	&& echo "deb http://ppa.launchpad.net/mozillateam/firefox-next/ubuntu xenial main" >> /etc/apt/sources.list.d/firefox.list \
+	&& echo "deb http://ppa.launchpad.net/mozillateam/firefox-next/ubuntu ${UBUVERSION} main" >> /etc/apt/sources.list.d/firefox.list \
 	&& apt-get update && apt-get install -y \
 	apulse \
 	ca-certificates \
@@ -23,7 +35,7 @@ RUN apt-get update && apt-get install -y \
 	--no-install-recommends \
 	&& rm -rf /var/lib/apt/lists/*
 
-ENV LANG en-US
+ENV LANG C.UTF-8
 
 COPY local.conf /etc/fonts/local.conf
 
@@ -31,4 +43,10 @@ RUN echo 'pref("browser.tabs.remote.autostart", false);' >> /etc/firefox/syspref
 
 COPY entrypoint.sh /usr/bin/startfirefox
 
+ARG USER=user
+ARG HOME=/home/${USER}
+RUN useradd --create-home --home-dir $HOME $USER && chown -R ${USER}:${USER} $HOME
+WORKDIR $HOME
+USER $USER
+
 ENTRYPOINT [ "startfirefox" ]