diff --git a/browser/components/sessionstore/test/browser.ini b/browser/components/sessionstore/test/browser.ini
index 579befaa5eb3..375d0b47bb25 100644
--- a/browser/components/sessionstore/test/browser.ini
+++ b/browser/components/sessionstore/test/browser.ini
@@ -97,6 +97,8 @@ skip-if = e10s
 [browser_sessionStorage.js]
 [browser_swapDocShells.js]
 skip-if = e10s # See bug 918634
+[browser_switch_remoteness.js]
+run-if = e10s
 [browser_telemetry.js]
 [browser_upgrade_backup.js]
 [browser_windowRestore_perwindowpb.js]
diff --git a/browser/components/sessionstore/test/browser_switch_remoteness.js b/browser/components/sessionstore/test/browser_switch_remoteness.js
new file mode 100644
index 000000000000..e670c37b3822
--- /dev/null
+++ b/browser/components/sessionstore/test/browser_switch_remoteness.js
@@ -0,0 +1,47 @@
+"use strict";
+
+const URL = "http://example.com/browser_switch_remoteness_";
+
+function countHistoryEntries(browser) {
+  return ContentTask.spawn(browser, null, function* () {
+    let Ci = Components.interfaces;
+    let webNavigation = docShell.QueryInterface(Ci.nsIWebNavigation);
+    let history = webNavigation.sessionHistory.QueryInterface(Ci.nsISHistoryInternal);
+    return history && history.count;
+  });
+}
+
+add_task(function* () {
+  // Add a new tab.
+  let tab = gBrowser.addTab("about:blank");
+  let browser = tab.linkedBrowser;
+  yield promiseBrowserLoaded(browser);
+  ok(browser.isRemoteBrowser, "browser is remote");
+
+  // Get the maximum number of preceding entries to save.
+  const MAX_BACK = Services.prefs.getIntPref("browser.sessionstore.max_serialize_back");
+  ok(MAX_BACK > -1, "check that the default has a value that caps data");
+
+  // Load more pages than we would save to disk on a clean shutdown.
+  for (let i = 0; i < MAX_BACK + 2; i++) {
+    browser.loadURI(URL + i);
+    yield promiseBrowserLoaded(browser);
+    ok(browser.isRemoteBrowser, "browser is still remote");
+  }
+
+  // Check we have the right number of shistory entries.
+  let count = yield countHistoryEntries(browser);
+  is(count, MAX_BACK + 2, "correct number of shistory entries");
+
+  // Load a non-remote page.
+  browser.loadURI("about:robots");
+  yield promiseTabRestored(tab);
+  ok(!browser.isRemoteBrowser, "browser is not remote anymore");
+
+  // Check that we didn't lose any shistory entries.
+  count = yield countHistoryEntries(browser);
+  is(count, MAX_BACK + 3, "correct number of shistory entries");
+
+  // Cleanup.
+  gBrowser.removeTab(tab);
+});
diff --git a/testing/mochitest/BrowserTestUtils/ContentTask.jsm b/testing/mochitest/BrowserTestUtils/ContentTask.jsm
index 3c4c2ff052a6..c824d07edc46 100644
--- a/testing/mochitest/BrowserTestUtils/ContentTask.jsm
+++ b/testing/mochitest/BrowserTestUtils/ContentTask.jsm
@@ -13,10 +13,7 @@ this.EXPORTED_SYMBOLS = [
 const { classes: Cc, interfaces: Ci, utils: Cu } = Components;
 Cu.import("resource://gre/modules/Promise.jsm");
 
-/**
- * Set of browsers which have loaded the content-task frame script.
- */
-let gScriptLoadedSet = new WeakSet();
+const FRAME_SCRIPT = "chrome://mochikit/content/tests/BrowserTestUtils/content-task.js";
 
 /**
  * Mapping from message id to associated promise.
@@ -50,12 +47,12 @@ this.ContentTask = {
    * @rejects An error message if execution fails.
    */
   spawn: function ContentTask_spawn(browser, arg, task) {
-    if(!gScriptLoadedSet.has(browser.permanentKey)) {
-      let mm = browser.messageManager;
-      mm.loadFrameScript(
-        "chrome://mochikit/content/tests/BrowserTestUtils/content-task.js", true);
+    let mm = browser.ownerDocument.defaultView.messageManager;
+    let scripts = mm.getDelayedFrameScripts();
 
-      gScriptLoadedSet.add(browser.permanentKey);
+    // Load the frame script if needed.
+    if (!scripts.find(script => script[0] == FRAME_SCRIPT)) {
+      mm.loadFrameScript(FRAME_SCRIPT, true);
     }
 
     let deferred = {};