diff --git a/testing/xpcshell/remotexpcshelltests.py b/testing/xpcshell/remotexpcshelltests.py
index 46539c80a7ea..f08cbf0c094e 100644
--- a/testing/xpcshell/remotexpcshelltests.py
+++ b/testing/xpcshell/remotexpcshelltests.py
@@ -25,12 +25,16 @@ class XPCShellRemote(xpcshell.XPCShellTests, object):
         self.device = devmgr
         self.pathMapping = []
         self.remoteTestRoot = self.device.getTestRoot("xpcshell")
-        # Terse directory names are used here ("b" for a binaries directory)
+        # remoteBinDir contains xpcshell and its wrapper script, both of which must
+        # be executable. Since +x permissions cannot usually be set on /mnt/sdcard,
+        # and the test root may be on /mnt/sdcard, remoteBinDir is set to be on 
+        # /data/local, always.
+        self.remoteBinDir = "/data/local/xpcb"
+        # Terse directory names are used here ("c" for the components directory)
         # to minimize the length of the command line used to execute
         # xpcshell on the remote device. adb has a limit to the number
         # of characters used in a shell command, and the xpcshell command
         # line can be quite complex.
-        self.remoteBinDir = self.remoteJoin(self.remoteTestRoot, "b")
         self.remoteTmpDir = self.remoteJoin(self.remoteTestRoot, "tmp")
         self.remoteScriptsDir = self.remoteTestRoot
         self.remoteComponentsDir = self.remoteJoin(self.remoteTestRoot, "c")
@@ -83,6 +87,10 @@ class XPCShellRemote(xpcshell.XPCShellTests, object):
         return local
 
     def setupUtilities(self):
+        if (not self.device.dirExists(self.remoteBinDir)):
+          # device.mkDir may fail here where shellCheckOutput may succeed -- see bug 817235
+          self.device.shellCheckOutput(["mkdir", self.remoteBinDir]);
+
         remotePrefDir = self.remoteJoin(self.remoteBinDir, "defaults/pref")
         if (self.device.dirExists(self.remoteTmpDir)):
           self.device.removeDir(self.remoteTmpDir)