diff --git a/firefox/Dockerfile b/firefox/Dockerfile
index 437ba2e..fa0ab81 100644
--- a/firefox/Dockerfile
+++ b/firefox/Dockerfile
@@ -1,7 +1,10 @@
 # syntax = docker/dockerfile:1
 FROM alpine/base:i3
 USER root
- 
+
+# Build ARG: use "root" for debugging
+ARG debug
+
 # Install packages
 RUN apk add --no-cache \
     firefox
@@ -9,5 +12,5 @@ RUN apk add --no-cache \
 # Tigervnc
 COPY *.sh /app/init.d/
 
-# Reset user home directory
-USER user
+# Reset user
+USER ${debug:-user}
\ No newline at end of file