diff -r 000000000000 -r 6474c204b198 modules/libjar/test/unit/head_ipc.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/modules/libjar/test/unit/head_ipc.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,17 @@
+/*
+ * If we're running in e10s, determines whether we're in child directory or
+ * not.
+ */
+
+var inChild = false;
+var filePrefix = "";
+try {
+  inChild = Components.classes["@mozilla.org/xre/runtime;1"].
+              getService(Components.interfaces.nsIXULRuntime).processType
+              != Components.interfaces.nsIXULRuntime.PROCESS_TYPE_DEFAULT;
+  if (inChild) {
+    // use "jar:remoteopenfile://" in child instead of "jar:file://"
+    filePrefix = "remoteopen";
+  }
+} 
+catch (e) { }