diff --git a/streaming/session-manager/src/docker.ts b/streaming/session-manager/src/docker.ts
index 981deec..32f7043 100644
--- a/streaming/session-manager/src/docker.ts
+++ b/streaming/session-manager/src/docker.ts
@@ -46,9 +46,7 @@ export class DockerDriver implements Driver {
         `PUID=${uid}`,
         `PGID=${gid}`,
         `SUBFOLDER=${streamPath(id)}`,
-        // The game's exact size, and the display's, rounded up to even for H.264
-        `GAME_WIDTH=${size.width}`,
-        `GAME_HEIGHT=${size.height}`,
+        // The game's size, rounded up to even for H.264
         `SELKIES_MANUAL_WIDTH=${size.width + (size.width % 2)}`,
         `SELKIES_MANUAL_HEIGHT=${size.height + (size.height % 2)}`,
         'SELKIES_UI_SHOW_SIDEBAR=false',
diff --git a/streaming/streamer/Dockerfile b/streaming/streamer/Dockerfile
index 3a95ceb..fa325bc 100644
--- a/streaming/streamer/Dockerfile
+++ b/streaming/streamer/Dockerfile
@@ -30,6 +30,7 @@ RUN apt-get update && \
     libxtst6 \
     libxxf86vm1 \
     sqlite3 \
+    x11-utils \
     xdotool && \
   rm -rf /var/lib/apt/lists/*
 
diff --git a/streaming/streamer/README.md b/streaming/streamer/README.md
index 1b0605a..ad1e4db 100644
--- a/streaming/streamer/README.md
+++ b/streaming/streamer/README.md
@@ -54,6 +54,8 @@ is Flash Player's save directory, so the session manager syncs both to the
 player's browser. OldCPUSimulator hangs under Wine, so its target runs under
 `cpulimit` at the same share of the CPU. A Flash projector's window is
 stretched to the display and moved up by its menu bar's height, which hides the
-menu bar; the height is the window's opening height less the movie's
-(`GAME_HEIGHT`). Its full-screen mode isn't used, since some games, such as
-Bloons, don't play right in it. Flashpoint Navigator's toolbars are hidden.
+menu bar. GTK draws the menu bar in the window itself and the movie in a child
+window below it, so the movie's offset, read with `xwininfo`, is the menu bar's
+height. The window is made override-redirect first, since the window manager
+keeps windows on screen. Its full-screen mode isn't used, since some games, such
+as Bloons, don't play right in it. Flashpoint Navigator's toolbars are hidden.
diff --git a/streaming/streamer/root/usr/local/bin/fp-launch b/streaming/streamer/root/usr/local/bin/fp-launch
index 8b327ff..b20c873 100755
--- a/streaming/streamer/root/usr/local/bin/fp-launch
+++ b/streaming/streamer/root/usr/local/bin/fp-launch
@@ -49,16 +49,28 @@ case ${app,,} in
     if [[ ${app,,} == 'fpsoftware\flash\'* ]]; then
       # Hide the projector's menu bar by moving it above the display, and fill
       # the display with the movie. Not full screen, which some games, such as
-      # Bloons, don't play right in. The window opens at the movie's size plus
-      # the menu bar, which gives the menu bar's height.
+      # Bloons, don't play right in. The window manager keeps windows on
+      # screen, so the window is taken out of its hands first.
       (
+        set +eo pipefail
         wid=$(xdotool search --sync --onlyvisible --name 'Flash Player' | head -1)
-        eval "$(xdotool getwindowgeometry --shell "$wid")"
-        read -r display_width display_height < <(xdotool getdisplaygeometry)
-        menu=$((HEIGHT - ${GAME_HEIGHT:-$display_height}))
-        ((menu > 0 && menu < 100)) || menu=0
-        xdotool windowsize "$wid" "$display_width" $((display_height + menu)) \
-          windowmove "$wid" 0 $((-menu)) windowactivate "$wid"
+        read -r width height < <(xdotool getdisplaygeometry)
+        # GTK draws the menu bar in the window itself, and the movie in the
+        # largest child window, below it: the movie's offset is the menu bar's height
+        menu=$(xwininfo -children -id "$wid" | awk '
+          match($0, /[0-9]+x[0-9]+\+-?[0-9]+\+-?[0-9]+/) {
+            split(substr($0, RSTART, RLENGTH), g, /[x+]/)
+            if (g[1] * g[2] > area) { area = g[1] * g[2]; top = g[4] }
+          }
+          END { print top + 0 }')
+        ((menu >= 0 && menu < height)) || menu=0
+        echo "Flash Player window $wid: menu bar ${menu}px, display ${width}x${height}"
+        xdotool windowunmap --sync "$wid"
+        xdotool set_window --overrideredirect 1 "$wid"
+        xdotool windowmap --sync "$wid"
+        xdotool windowsize "$wid" "$width" $((height + menu)) \
+          windowmove "$wid" 0 $((-menu)) windowfocus "$wid"
+        xdotool getwindowgeometry "$wid"
       ) &
     fi
     cd "${argv[0]}"