--- a/testing/xpcshell/remotexpcshelltests.py
+++ b/testing/xpcshell/remotexpcshelltests.py
@@ -174,23 +174,36 @@ class XPCShellRemote(xpcshell.XPCShellTe
 
         if self.remoteDebugger:
           # for example, "/data/local/gdbserver" "localhost:12345"
           self.xpcsCmd = [
             self.remoteDebugger, 
             self.remoteDebuggerArgs, 
             self.xpcsCmd]
 
-    def getHeadFiles(self, test):
+    def getHeadAndTailFiles(self, test):
+        """Override parent method to find files on remote device."""
+        def sanitize_list(s, kind):
+            for f in s.strip().split(' '):
+                f = f.strip()
+                if len(f) < 1:
+                    continue
+
+                path = self.remoteJoin(self.remoteHere, f)
+                if not self.device.fileExists(path):
+                    raise Exception('%s file does not exist: %s' % ( kind,
+                        path))
+
+                yield path
+
         self.remoteHere = self.remoteForLocal(test['here'])
-        return [f.strip() for f in sorted(test['head'].split(' ')) if self.device.fileExists(self.remoteJoin(self.remoteHere, f))]
-    
-    def getTailFiles(self, test):
-        return [f.strip() for f in sorted(test['tail'].split(' ')) if self.device.fileExists(self.remoteJoin(self.remoteHere, f))]
-        
+
+        return (list(sanitize_list(test['head'], 'head')),
+                list(sanitize_list(test['tail'], 'tail')))
+
     def buildCmdTestFile(self, name):
         remoteDir = self.remoteForLocal(os.path.dirname(name))
         if remoteDir == self.remoteHere:
           remoteName = os.path.basename(name)
         else:
           remoteName = self.remoteJoin(remoteDir, os.path.basename(name))
         return ['-e', 'const _TEST_FILE = ["%s"];' %
                  replaceBackSlashes(remoteName)]

--- a/testing/xpcshell/runxpcshelltests.py
+++ b/testing/xpcshell/runxpcshelltests.py
@@ -249,34 +249,39 @@ class XPCShellTests(object):
           self.testPath = self.testPath.rsplit('/', 1)
           self.singleFile = self.testPath[1]
           self.testPath = self.testPath[0]
       else:
         # Path only.
         # Simply remove optional ending separator.
         self.testPath = self.testPath.rstrip("/")
 
+  def getHeadAndTailFiles(self, test):
+      """Obtain the list of head and tail files.
 
-  def getHeadFiles(self, test):
-    """
-      test['head'] is a whitespace delimited list of head files.
-      return the list of head files as paths including the subdir if the head file exists
+      Returns a 2-tuple. The first element is a list of head files. The second
+      is a list of tail files.
+      """
+      def sanitize_list(s, kind):
+          for f in s.strip().split(' '):
+              f = f.strip()
+              if len(f) < 1:
+                  continue
 
-      On a remote system, this may be overloaded to list files in a remote directory structure.
-    """
-    return [os.path.join(test['here'], f).strip() for f in sorted(test['head'].split(' ')) if os.path.isfile(os.path.join(test['here'], f))]
+              path = os.path.normpath(os.path.join(test['here'], f))
+              if not os.path.exists(path):
+                  raise Exception('%s file does not exist: %s' % (kind, path))
 
-  def getTailFiles(self, test):
-    """
-      test['tail'] is a whitespace delimited list of head files.
-      return the list of tail files as paths including the subdir if the tail file exists
+              if not os.path.isfile(path):
+                  raise Exception('%s file is not a file: %s' % (kind, path))
 
-      On a remote system, this may be overloaded to list files in a remote directory structure.
-    """
-    return [os.path.join(test['here'], f).strip() for f in sorted(test['tail'].split(' ')) if os.path.isfile(os.path.join(test['here'], f))]
+              yield path
+
+      return (list(sanitize_list(test['head'], 'head')),
+              list(sanitize_list(test['tail'], 'tail')))
 
   def setupProfileDir(self):
     """
       Create a temporary folder for the profile and set appropriate environment variables.
       When running check-interactive and check-one, the directory is well-defined and
       retained for inspection once the tests complete.
 
       On a remote system, this may be overloaded to use a remote path structure.
@@ -632,18 +637,17 @@ class XPCShellTests(object):
         xunitResults.append(xunitResult)
         continue
 
       # Check for known-fail tests
       expected = test['expected'] == 'pass'
 
       testdir = os.path.dirname(name)
       self.buildXpcsCmd(testdir)
-      testHeadFiles = self.getHeadFiles(test)
-      testTailFiles = self.getTailFiles(test)
+      testHeadFiles, testTailFiles = self.getHeadAndTailFiles(test)
       cmdH = self.buildCmdHead(testHeadFiles, testTailFiles, self.xpcsCmd)
 
       # create a temp dir that the JS harness can stick a profile in
       self.profileDir = self.setupProfileDir()
       self.leakLogFile = self.setupLeakLogging()
 
       # The test file will have to be loaded after the head files.
       cmdT = self.buildCmdTestFile(name)

--- a/testing/xpcshell/selftest.py
+++ b/testing/xpcshell/selftest.py
@@ -207,16 +207,51 @@ tail =
         self.assertTestResult(False)
         self.assertEquals(1, self.x.testCount)
         self.assertEquals(0, self.x.passCount)
         self.assertEquals(1, self.x.failCount)
         self.assertEquals(0, self.x.todoCount)
         self.assertInLog("TEST-UNEXPECTED-FAIL")
         self.assertNotInLog("TEST-PASS")
 
+    def testMissingHeadFile(self):
+        """
+        Ensure that missing head file results in fatal error.
+        """
+        self.writeFile("test_basic.js", SIMPLE_PASSING_TEST)
+        self.writeManifest([("test_basic.js", "head = missing.js")])
+
+        raised = False
+
+        try:
+            # The actual return value is never checked because we raise.
+            self.assertTestResult(True)
+        except Exception, ex:
+            raised = True
+            self.assertEquals(ex.message[0:9], "head file")
+
+        self.assertTrue(raised)
+
+    def testMissingTailFile(self):
+        """
+        Ensure that missing tail file results in fatal error.
+        """
+        self.writeFile("test_basic.js", SIMPLE_PASSING_TEST)
+        self.writeManifest([("test_basic.js", "tail = missing.js")])
+
+        raised = False
+
+        try:
+            self.assertTestResult(True)
+        except Exception, ex:
+            raised = True
+            self.assertEquals(ex.message[0:9], "tail file")
+
+        self.assertTrue(raised)
+
     def testRandomExecution(self):
         """
         Check that random execution doesn't break.
         """
         manifest = []
         for i in range(0, 10):
             filename = "test_pass_%d.js" % i
             self.writeFile(filename, SIMPLE_PASSING_TEST)

--- a/toolkit/crashreporter/test/unit_ipc/xpcshell.ini
+++ b/toolkit/crashreporter/test/unit_ipc/xpcshell.ini
@@ -1,5 +1,5 @@
 [DEFAULT]
-head = head_crashreporter.js
-tail = 
+head =
+tail =
 
 [test_content_annotation.js]