I'm sooo sorry! I thought the screenshot provide would've given you that data. Maybe it didn't properly post.
Anyways, I installed with:
mkdir /home/geek_diruendis/firefox
docker run --name Firefox -d \
-p 8080:8080 \
--env 'FIREFOX_V=latest' \
--env 'FIREFOX_LANG=en-US' \
--env 'CUSTOM_RES_W=1280' \
--env 'CUSTOM_RES_H=768' \
--env 'UID=99' \
--env 'GID=100' \
--env 'UMASK=000' \
--env 'DATA_PERM=770' \
--volume /home/geek_diruendis/firefox:/firefox \
ich777/firefox
(i've also tried swapping UID & GID for PUID & PGID to both = 1000, because I've found my other containers work better with that in the past.)
Then, I opened the FireFox-specific container's terminal (via from the web interface), then typed and got the following:
root@c7a6e9c08385:/# su $USER
firefox@c7a6e9c08385:/$ vncpasswd
bash: vncpasswd: command not found
firefox@c7a6e9c08385:/$ exit
exit
root@c7a6e9c08385:/# vncpasswd
bash: vncpasswd: command not found
root@c7a6e9c08385:/#