--- a/layout/tools/reftest/reftestcommandline.py
+++ b/layout/tools/reftest/reftestcommandline.py
@@ -273,29 +273,30 @@ class ReftestArgumentsParser(argparse.Ar
                 self.error("--xre-path '%s' not found" % options.xrePath)
             if not os.path.isdir(options.xrePath):
                 self.error("--xre-path '%s' is not a directory" %
                            options.xrePath)
             options.xrePath = reftest.getFullPath(options.xrePath)
 
         if options.reftestExtensionPath is None:
             if self.build_obj is not None:
-                options.reftestExtensionPath = os.path.join(self.build_obj.topobjdir, "_tests",
-                                                            "reftest", "reftest")
+                reftestExtensionPath = os.path.join(self.build_obj.topobjdir, "_tests",
+                                                    "reftest", "reftest")
             else:
-                options.reftestExtensionPath = os.path.join(here, "reftest")
+                reftestExtensionPath = os.path.join(here, "reftest")
+            options.reftestExtensionPath = os.path.normpath(reftestExtensionPath)
 
         if (options.specialPowersExtensionPath is None and
             options.suite in ["crashtest", "jstestbrowser"]):
             if self.build_obj is not None:
-                options.specialPowersExtensionPath = os.path.join(self.build_obj.topobjdir, "_tests",
-                                                                  "reftest", "specialpowers")
+                specialPowersExtensionPath = os.path.join(self.build_obj.topobjdir, "_tests",
+                                                          "reftest", "specialpowers")
             else:
-                options.specialPowersExtensionPath = os.path.join(
-                    here, "specialpowers")
+                specialPowersExtensionPath = os.path.join(here, "specialpowers")
+            options.specialPowersExtensionPath = os.path.normpath(specialPowersExtensionPath)
 
         options.leakThresholds = {
             "default": options.defaultLeakThreshold,
             "tab": 5000,  # See dependencies of bug 1051230.
         }
 
 
 class DesktopArgumentsParser(ReftestArgumentsParser):