install window manager ratpoison to maximize browser window

Dockerfile

@@ -2,11 +2,13 @@ FROM ubuntu:18.04
 
 RUN apt-get update && apt-get install --yes --no-install-recommends \
     firefox \
+    ratpoison `# window manager` \
     x11vnc \
     xvfb
 
 RUN useradd --create-home vnc
 COPY --chown=vnc xinitrc /home/vnc/.xinitrc
+COPY --chown=vnc ratpoisonrc /home/vnc/.ratpoisonrc
 USER vnc
 EXPOSE 5900/tcp
 ENV X11VNC_CREATE_GEOM 1920x1080

ratpoisonrc

@@ -0,0 +1 @@
+exec firefox

xinitrc

@@ -1 +1 @@
-exec firefox
+exec ratpoison