diff -r b3a192804b63 -r 941e3d15c338 devtools/qunit.py
--- a/devtools/qunit.py	Mon Aug 24 14:33:14 2015 +0200
+++ b/devtools/qunit.py	Tue Sep 01 17:13:16 2015 +0200
@@ -17,8 +17,9 @@
 # with CubicWeb.  If not, see <http://www.gnu.org/licenses/>.
 
 import os, os.path as osp
+import errno
 from tempfile import mkdtemp
-from subprocess import Popen
+from subprocess import Popen, PIPE, STDOUT
 
 from six.moves.queue import Queue, Empty
 
@@ -42,6 +43,17 @@
             self.firefox_cmd = [osp.join(osp.dirname(__file__), 'data', 'xvfb-run.sh'),
                                 '-a', '-s', '-noreset -screen 0 800x600x24'] + self.firefox_cmd
 
+    def test(self):
+        try:
+            proc = Popen(['firefox', '--help'], stdout=PIPE, stderr=STDOUT)
+            stdout, _ = proc.communicate()
+            return proc.returncode == 0, stdout
+        except OSError as exc:
+            if exc.errno == errno.ENOENT:
+                msg = '[%s] %s' % (errno.errorcode[exc.errno], exc.strerror)
+                return False, msg
+            raise
+
     def start(self, url):
         self.stop()
         cmd = self.firefox_cmd + ['-silent', '--profile', self._profile_dir,
@@ -116,6 +128,9 @@
             self.test_queue.get(False)
 
         browser = FirefoxHelper()
+        isavailable, reason = browser.test()
+        if not isavailable:
+            self.fail('firefox not available or not working properly (%s)' % reason)
         browser.start(self.config['base-url'] + "?vid=qunit")
         test_count = 0
         error = False