diff -r 000000000000 -r 6474c204b198 xpcom/threads/nsIEnvironment.idl
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/threads/nsIEnvironment.idl	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,55 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+
+/**
+ * Scriptable access to the current process environment.
+ *
+ */
+[scriptable, uuid(101d5941-d820-4e85-a266-9a3469940807)]
+interface nsIEnvironment : nsISupports
+{
+    /**
+     * Set the value of an environment variable.
+     *
+     * @param aName   the variable name to set.
+     * @param aValue  the value to set.
+     */
+    void set(in AString aName, in AString aValue);
+
+    /**
+     * Get the value of an environment variable.
+     *
+     * @param aName   the variable name to retrieve.
+     * @return        returns the value of the env variable. An empty string
+     *                will be returned when the env variable does not exist or
+     *                when the value itself is an empty string - please use
+     *                |exists()| to probe whether the env variable exists
+     *                or not.
+     */
+    AString get(in AString aName);
+
+    /**
+     * Check the existence of an environment variable.
+     * This method checks whether an environment variable is present in
+     * the environment or not.
+     *
+     * - For Unix/Linux platforms we follow the Unix definition:
+     * An environment variable exists when |getenv()| returns a non-NULL value.
+     * An environment variable does not exist when |getenv()| returns NULL.
+     * - For non-Unix/Linux platforms we have to fall back to a 
+     * "portable" definition (which is incorrect for Unix/Linux!!!!)
+     * which simply checks whether the string returned by |Get()| is empty
+     * or not.
+     *
+     * @param aName   the variable name to probe.
+     * @return        if the variable has been set, the value returned is
+     *                PR_TRUE. If the variable was not defined in the
+     *                environment PR_FALSE will be returned.
+     */
+    boolean exists(in AString aName);
+};
+