1 files changed, 50 insertions, 0 deletions
diff --git a/browser/base/content/test/general/browser_bug623893.js b/browser/base/content/test/general/browser_bug623893.js
new file mode 100644
index 0000000000..27751e74ad
--- /dev/null
+++ b/browser/base/content/test/general/browser_bug623893.js
@@ -0,0 +1,50 @@
+add_task(async function test() {
+  await BrowserTestUtils.withNewTab(
+    "data:text/plain;charset=utf-8,1",
+    async function (browser) {
+      BrowserTestUtils.loadURIString(
+        browser,
+        "data:text/plain;charset=utf-8,2"
+      );
+      await BrowserTestUtils.browserLoaded(browser);
+
+      BrowserTestUtils.loadURIString(
+        browser,
+        "data:text/plain;charset=utf-8,3"
+      );
+      await BrowserTestUtils.browserLoaded(browser);
+
+      await duplicate(0, "maintained the original index");
+      BrowserTestUtils.removeTab(gBrowser.selectedTab);
+
+      await duplicate(-1, "went back");
+      await duplicate(1, "went forward");
+      BrowserTestUtils.removeTab(gBrowser.selectedTab);
+      BrowserTestUtils.removeTab(gBrowser.selectedTab);
+    }
+  );
+});
+
+async function promiseGetIndex(browser) {
+  if (!SpecialPowers.Services.appinfo.sessionHistoryInParent) {
+    return SpecialPowers.spawn(browser, [], function () {
+      let shistory =
+        docShell.browsingContext.childSessionHistory.legacySHistory;
+      return shistory.index;
+    });
+  }
+
+  let shistory = browser.browsingContext.sessionHistory;
+  return shistory.index;
+}
+
+let duplicate = async function (delta, msg, cb) {
+  var startIndex = await promiseGetIndex(gBrowser.selectedBrowser);
+
+  duplicateTabIn(gBrowser.selectedTab, "tab", delta);
+
+  await BrowserTestUtils.waitForEvent(gBrowser.tabContainer, "SSTabRestored");
+
+  let endIndex = await promiseGetIndex(gBrowser.selectedBrowser);
+  is(endIndex, startIndex + delta, msg);
+};