--- a/taskcluster/docker/desktop-build/Dockerfile
+++ b/taskcluster/docker/desktop-build/Dockerfile
@@ -65,16 +65,16 @@ ADD           oauth.txt /home/worker/
 # the directory where mozharness is run (not its --work-dir)
 ADD           buildprops.json /home/worker/
 
 # Move installation to base centos6-build image once Bug 1272629 is fixed
 # Install the screen package here to use with xvfb.
 # Install bison to build binutils.
 RUN yum install -y bison screen
 
-# For the mingw toolchain (nsis and wine)
-RUN yum install -y scons flex
+# For the mingw toolchain & job (scons: nsis, flex: wine, p7zip: ff installer)
+RUN yum install -y scons flex p7zip
 
 # Install libtool.
 RUN yum install -y libtool
 
 # Set a default command useful for debugging
 CMD ["/bin/bash", "--login"]