Backed out changeset 835fbe63da4a (bug 1076446) for perma failure in 10.8 mozilla-inbound debug test xpcshell

testing/xpcshell/runxpcshelltests.py

@@ -620,10 +620,10 @@ class XPCShellTestThread(Thread):
                 preloadEnvVar = 'MOZ_REPLACE_MALLOC_LIB'
                 libdmd = os.path.join(self.xrePath, 'dmd.dll')
 
+            self.env['DMD'] = '--mode=test'
             self.env['PYTHON'] = sys.executable
             self.env['BREAKPAD_SYMBOLS_PATH'] = self.symbolsPath
-            self.env['DMD_PRELOAD_VAR'] = preloadEnvVar
-            self.env['DMD_PRELOAD_VALUE'] = libdmd
+            self.env[preloadEnvVar] = libdmd
 
         testTimeoutInterval = HARNESS_TIMEOUT
         # Allow a test to request a multiple of the timeout if it is expected to take long