diff -r 000000000000 -r 6474c204b198 browser/components/sessionstore/test/browser_467409-backslashplosion.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/components/sessionstore/test/browser_467409-backslashplosion.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,77 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test Summary:
+// 1.  Open about:sessionrestore where formdata is a JS object, not a string
+// 1a. Check that #sessionData on the page is readable after JSON.parse (skipped, checking formdata is sufficient)
+// 1b. Check that there are no backslashes in the formdata
+// 1c. Check that formdata doesn't require JSON.parse
+//
+// 2.  Use the current state (currently about:sessionrestore with data) and then open that in a new instance of about:sessionrestore
+// 2a. Check that there are no backslashes in the formdata
+// 2b. Check that formdata doesn't require JSON.parse
+//
+// 3.  [backwards compat] Use a stringified state as formdata when opening about:sessionrestore
+// 3a. Make sure there are nodes in the tree on about:sessionrestore (skipped, checking formdata is sufficient)
+// 3b. Check that there are no backslashes in the formdata
+// 3c. Check that formdata doesn't require JSON.parse
+
+const CRASH_STATE = {windows: [{tabs: [{entries: [{url: "about:mozilla" }]}]}]};
+const STATE = {entries: [createEntry(CRASH_STATE)]};
+const STATE2 = {entries: [createEntry({windows: [{tabs: [STATE]}]})]};
+const STATE3 = {entries: [createEntry(JSON.stringify(CRASH_STATE))]};
+
+function createEntry(sessionData) {
+  return {
+    url: "about:sessionrestore",
+    formdata: {id: {sessionData: sessionData}}
+  };
+}
+
+add_task(function test_nested_about_sessionrestore() {
+  // Prepare a blank tab.
+  let tab = gBrowser.addTab("about:blank");
+  let browser = tab.linkedBrowser;
+  yield promiseBrowserLoaded(browser);
+
+  // test 1
+  ss.setTabState(tab, JSON.stringify(STATE));
+  yield promiseTabRestored(tab);
+  checkState("test1", tab);
+
+  // test 2
+  ss.setTabState(tab, JSON.stringify(STATE2));
+  yield promiseTabRestored(tab);
+  checkState("test2", tab);
+
+  // test 3
+  ss.setTabState(tab, JSON.stringify(STATE3));
+  yield promiseTabRestored(tab);
+  checkState("test3", tab);
+
+  // Cleanup.
+  gBrowser.removeTab(tab);
+});
+
+function checkState(prefix, tab) {
+  // Flush and query tab state.
+  SyncHandlers.get(tab.linkedBrowser).flush();
+  let {formdata} = JSON.parse(ss.getTabState(tab));
+
+  ok(formdata.id["sessionData"], prefix + ": we have form data for about:sessionrestore");
+
+  let sessionData_raw = JSON.stringify(formdata.id["sessionData"]);
+  ok(!/\\/.test(sessionData_raw), prefix + ": #sessionData contains no backslashes");
+  info(sessionData_raw);
+
+  let gotError = false;
+  try {
+    JSON.parse(formdata.id["sessionData"]);
+  } catch (e) {
+    info(prefix + ": got error: " + e);
+    gotError = true;
+  }
+  ok(gotError, prefix + ": attempting to JSON.parse form data threw error");
+}