diff --git a/browser/base/content/tabbrowser.xml b/browser/base/content/tabbrowser.xml
index dddc2164f78..17137d86aa5 100644
--- a/browser/base/content/tabbrowser.xml
+++ b/browser/base/content/tabbrowser.xml
@@ -1498,7 +1498,7 @@
             aBrowser.setAttribute("remote", aShouldBeRemote ? "true" : "false");
             // Tearing down the browser gives a new permanentKey but we want to
             // keep the old one. Re-set it explicitly after unbinding from DOM.
-            aBrowser.permanentKey = permanentKey;
+            aBrowser._permanentKey = permanentKey;
             parent.appendChild(aBrowser);
 
             // Restore the progress listener.
diff --git a/browser/base/content/test/general/browser.ini b/browser/base/content/test/general/browser.ini
index 209c444bb22..f34c8b21ce7 100644
--- a/browser/base/content/test/general/browser.ini
+++ b/browser/base/content/test/general/browser.ini
@@ -412,6 +412,7 @@ skip-if = buildapp == 'mulet' || e10s
 [browser_tabMatchesInAwesomebar.js]
 [browser_tabMatchesInAwesomebar_perwindowpb.js]
 skip-if = e10s || os == 'linux' # Bug 1093373, bug 1104755
+[browser_tab_detach_restore.js]
 [browser_tab_drag_drop_perwindow.js]
 skip-if = buildapp == 'mulet'
 [browser_tab_dragdrop.js]
diff --git a/browser/base/content/test/general/browser_tab_detach_restore.js b/browser/base/content/test/general/browser_tab_detach_restore.js
new file mode 100644
index 00000000000..804be0869d7
--- /dev/null
+++ b/browser/base/content/test/general/browser_tab_detach_restore.js
@@ -0,0 +1,31 @@
+"use strict";
+
+add_task(function*() {
+  let uri = "http://example.com/browser/browser/base/content/test/general/dummy_page.html";
+
+  // Clear out the closed windows set to start
+  while (SessionStore.getClosedWindowCount() > 0)
+    SessionStore.forgetClosedWindow(0);
+
+  let tab = gBrowser.addTab();
+  tab.linkedBrowser.loadURI(uri);
+  yield BrowserTestUtils.browserLoaded(tab.linkedBrowser);
+
+  let key = tab.linkedBrowser.permanentKey;
+  let win = gBrowser.replaceTabWithWindow(tab);
+  yield new Promise(resolve => whenDelayedStartupFinished(win, resolve));
+
+  is(win.gBrowser.selectedBrowser.permanentKey, key, "Should have properly copied the permanentKey");
+  yield promiseWindowClosed(win);
+
+  is(SessionStore.getClosedWindowCount(), 1, "Should have restore data for the closed window");
+
+  win = SessionStore.undoCloseWindow(0);
+  yield BrowserTestUtils.waitForEvent(win, "load");
+  yield BrowserTestUtils.waitForEvent(win.gBrowser.tabs[0], "SSTabRestored");
+
+  is(win.gBrowser.tabs.length, 1, "Should have restored one tab");
+  is(win.gBrowser.selectedBrowser.currentURI.spec, uri, "Should have restored the right page");
+
+  yield promiseWindowClosed(win);
+});
diff --git a/toolkit/content/widgets/browser.xml b/toolkit/content/widgets/browser.xml
index e42c917683e..e2d968db332 100644
--- a/toolkit/content/widgets/browser.xml
+++ b/toolkit/content/widgets/browser.xml
@@ -388,9 +388,8 @@
 
       <field name="_permanentKey">({})</field>
 
-      <property name="permanentKey"
-                onget="return this._permanentKey;"
-                onset="this._permanentKey = val;"/>
+      <property name="permanentKey" readonly="true"
+                onget="return this._permanentKey;"/>
 
       <property name="outerWindowID" readonly="true">
         <getter><![CDATA[