--- a/ipc/glue/GeckoChildProcessHost.cpp
+++ b/ipc/glue/GeckoChildProcessHost.cpp
@@ -378,25 +378,25 @@ GeckoChildProcessHost::PerformAsyncLaunc
   setChildLogName.Append(origLogName);
 
   // remember original value so we can restore it.
   // - buffer needs to be permanently allocated for PR_SetEnv()
   // - Note: this code is not called re-entrantly, nor are restoreOrigLogName
   //   or mChildCounter touched by any other thread, so this is safe.
   static char* restoreOrigLogName = 0;
   if (!restoreOrigLogName)
-    restoreOrigLogName = strdup(PromiseFlatCString(setChildLogName).get());
+    restoreOrigLogName = strdup(setChildLogName.get());
 
   // Append child-specific postfix to name
   setChildLogName.AppendLiteral(".child-");
   setChildLogName.AppendInt(++mChildCounter);
 
   // Passing temporary to PR_SetEnv is ok here because env gets copied
   // by exec, etc., to permanent storage in child when process launched.
-  PR_SetEnv(PromiseFlatCString(setChildLogName).get());
+  PR_SetEnv(setChildLogName.get());
   bool retval = PerformAsyncLaunchInternal(aExtraOpts, arch);
 
   // Revert to original value
   PR_SetEnv(restoreOrigLogName);
 
   return retval;
 }