diff --git a/.devcontainer/Dockerfile b/.devcontainer/Dockerfile
index 0b844def..38dd492b 100644
--- a/.devcontainer/Dockerfile
+++ b/.devcontainer/Dockerfile
@@ -1,3 +1,33 @@
+#
+# Stage 0: Build xserver-xorg-video-dummy 0.3.8-2 with RandR support.
+#
+FROM debian:bullseye-slim as xserver-xorg-video-dummy
+
+WORKDIR /usr/local/src
+
+ENV DEBIAN_FRONTEND=noninteractive
+RUN set -eux; \
+    cp /etc/apt/sources.list /etc/apt/sources.list~; \
+    sed -Ei 's/^deb /deb-src /' /etc/apt/sources.list; \
+    cat /etc/apt/sources.list~ >> /etc/apt/sources.list; \
+    apt-get update; \
+    apt-get install -y dpkg-dev git; \
+    apt-get build-dep -y xserver-xorg-video-dummy; \
+    git clone --depth 1 --branch xserver-xorg-video-dummy-1_0.3.8-2 https://salsa.debian.org/xorg-team/driver/xserver-xorg-video-dummy; \
+    #
+    # clean up
+    apt-get clean -y; \
+    rm -rf /var/lib/apt/lists/* /var/cache/apt/*
+
+COPY runtime/xdummy-randr.patch /tmp/xdummy-randr.patch
+
+RUN set -eux; \
+    cd xserver-xorg-video-dummy; \
+    patch -p1 < /tmp/xdummy-randr.patch; \
+    bash ./autogen.sh; \
+    make; \
+    make install;
+
 # See here for image contents: https://github.com/microsoft/vscode-dev-containers/tree/v0.166.0/containers/go/.devcontainer/base.Dockerfile
 
 # [Choice] Go version: 1, 1.16, 1.15
@@ -13,7 +43,11 @@ RUN if [ "${INSTALL_NODE}" = "true" ]; then su vscode -c "umask 0002 && . /usr/l
 RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
     && apt-get -y install --no-install-recommends \
         libx11-dev libxrandr-dev libxtst-dev libgtk-3-dev \
-        libgstreamer1.0-dev libgstreamer-plugins-base1.0-dev
+        libgstreamer1.0-dev libgstreamer-plugins-base1.0-dev; \
+    # install libxcvt-dev (not available in debian:bullseye)
+    wget http://ftp.de.debian.org/debian/pool/main/libx/libxcvt/libxcvt-dev_0.1.2-1_amd64.deb; \
+    wget http://ftp.de.debian.org/debian/pool/main/libx/libxcvt/libxcvt0_0.1.2-1_amd64.deb; \
+    apt-get install  --no-install-recommends ./libxcvt0_0.1.2-1_amd64.deb ./libxcvt-dev_0.1.2-1_amd64.deb;
 
 # runtime dependencies
 RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
@@ -25,13 +59,14 @@ RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
         # needed for profile upload preStop hook
         zip curl \
         #
-        # file chooser handler, clipboard
-        xdotool xclip \
+        # file chooser handler, clipboard, drop
+        xdotool xclip libgtk-3-0 \
         #
         # gst
         gstreamer1.0-plugins-base gstreamer1.0-plugins-good \
         gstreamer1.0-plugins-bad gstreamer1.0-plugins-ugly \
         gstreamer1.0-pulseaudio;
+    # libxcvt already installed
 
 # dev runtime dependencies
 RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
@@ -55,10 +90,6 @@ RUN set -eux; \
     echo $USERNAME ALL=\(root\) NOPASSWD:ALL > /etc/sudoers.d/$USERNAME; \
     chmod 0440 /etc/sudoers.d/$USERNAME; \
     #
-    # setup pulseaudio
-    mkdir -p /home/$USERNAME/.config/pulse/; \
-    echo "default-server=unix:/tmp/pulseaudio.socket" > /home/$USERNAME/.config/pulse/client.conf; \
-    #
     # workaround for an X11 problem: http://blog.tigerteufel.de/?p=476
     mkdir /tmp/.X11-unix; \
     chmod 1777 /tmp/.X11-unix; \
@@ -81,6 +112,9 @@ RUN set -eux; \
         # Indian fonts
         fonts-indic;
 
+# replace version
+COPY --from=xserver-xorg-video-dummy /usr/local/lib/xorg/modules/drivers/dummy_drv.so /usr/lib/xorg/modules/drivers/dummy_drv.so
+
 # copy runtime files
 COPY runtime/dbus /usr/bin/dbus
 COPY runtime/default.pa /etc/pulse/default.pa
@@ -103,5 +137,6 @@ RUN chmod +x /usr/bin/dbus;\
 # set default envs
 ENV USER=$USERNAME
 ENV DISPLAY=:99.0
+ENV PULSE_SERVER=unix:/tmp/pulseaudio.socket
 ENV NEKO_SERVER_BIND=:3000
 ENV NEKO_WEBRTC_EPR=3001-3004
diff --git a/Dockerfile b/Dockerfile
index f1ea73a4..1c8db9a6 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -11,7 +11,7 @@ RUN set -eux; \
     sed -Ei 's/^deb /deb-src /' /etc/apt/sources.list; \
     cat /etc/apt/sources.list~ >> /etc/apt/sources.list; \
     apt-get update; \
-	apt-get install -y dpkg-dev git; \
+    apt-get install -y dpkg-dev git; \
     apt-get build-dep -y xserver-xorg-video-dummy; \
     git clone --depth 1 --branch xserver-xorg-video-dummy-1_0.3.8-2 https://salsa.debian.org/xorg-team/driver/xserver-xorg-video-dummy; \
     #
@@ -24,8 +24,8 @@ COPY runtime/xdummy-randr.patch /tmp/xdummy-randr.patch
 RUN set -eux; \
     cd xserver-xorg-video-dummy; \
     patch -p1 < /tmp/xdummy-randr.patch; \
-	bash ./autogen.sh; \
-	make; \
+    bash ./autogen.sh; \
+    make; \
     make install;
 
 #