Add test support for firefox
diff --git a/.travis.yml b/.travis.yml
index d3bd604..e746676 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -4,4 +4,7 @@
   - stable
   - dev
   - 1.21.0
+env:
+  - TEST_PLATFORM=vm
+  - TEST_PLATFORM=firefox
 script: ./tool/presubmit.sh
diff --git a/tool/presubmit.sh b/tool/presubmit.sh
index 364bee7..f1c7a23 100755
--- a/tool/presubmit.sh
+++ b/tool/presubmit.sh
@@ -26,4 +26,13 @@
 # Fail on anything that fails going forward.
 set -e
 
+THE_COMMAND="pub run test -p $TEST_PLATFORM"
+if [ $TEST_PLATFORM == 'firefox' ]; then
+  export DISPLAY=:99.0
+  sh -e /etc/init.d/xvfb start
+  t=0; until (xdpyinfo -display :99 &> /dev/null || test $t -gt 10); do sleep 1; let t=$t+1; done
+fi
+echo $THE_COMMAND
+exec $THE_COMMAND
+
 pub run test