--- a/browser/modules/BrowserUsageTelemetry.jsm
+++ b/browser/modules/BrowserUsageTelemetry.jsm
@@ -603,16 +603,19 @@ let BrowserUsageTelemetry = {
     win.removeEventListener("TabClose", this, true);
 
     // Don't include URI and domain counts when in private mode.
     if (PrivateBrowsingUtils.isWindowPrivate(win.defaultView)) {
       return;
     }
     win.defaultView.gBrowser.tabContainer.removeEventListener(TAB_RESTORING_TOPIC, this);
     win.defaultView.gBrowser.removeTabsProgressListener(URICountListener);
+
+    let tabCount = getOpenTabsAndWinsCounts().tabCount;
+    this._recordTabCount(tabCount);
   },
 
   /**
    * Updates the tab counts.
    * @param {Number} [newTabCount=0] The count of the opened tabs across all windows. This
    *        is computed manually if not provided.
    */
   _onTabOpen(tabCount = 0) {

--- a/browser/modules/test/browser/browser_UsageTelemetry.js
+++ b/browser/modules/test/browser/browser_UsageTelemetry.js
@@ -343,14 +343,17 @@ add_task(async function test_tabsHistogr
     ok(BrowserUsageTelemetry._lastRecordTabCount != oldLastRecordTabCount, "TAB_COUNT telemetry - _lastRecordTabCount updated");
     ok(BrowserUsageTelemetry._lastRecordTabCount > new Date().getTime() - BrowserUsageTelemetry._tabCountIntervalMillis, "TAB_COUNT telemetry - _lastRecordTabCount invariant");
   }
 
   BrowserUsageTelemetry._lastRecordTabCount = 0;
   await BrowserTestUtils.removeTab(openedTabs2.pop());
   checkTabCountHistogram(tabCountHist.snapshot(), [0,0,1,2,1,1,1,2], "TAB_COUNT telemetry - closing a tab");
 
+  BrowserUsageTelemetry._lastRecordTabCount = 0;
+  await BrowserTestUtils.closeWindow(win);
+  checkTabCountHistogram(tabCountHist.snapshot(), [0,0,1,2,2,1,1,2], "TAB_COUNT telemetry - closing a window");
+
   // Remove all the extra windows and tabs.
   for (let tab of openedTabs) {
     await BrowserTestUtils.removeTab(tab);
   }
-  await BrowserTestUtils.closeWindow(win);
 });