diff --git a/tabs-tabs-tabs/background.js b/tabs-tabs-tabs/background.js
new file mode 100644
index 0000000..ec4b051
--- /dev/null
+++ b/tabs-tabs-tabs/background.js
@@ -0,0 +1,28 @@
+function updateCount(tabId, isOnRemoved) {
+  browser.tabs.query({})
+  .then((tabs) => {
+    let length = tabs.length;
+
+    // onRemoved fires too early and the count is one too many.
+    // see https://bugzilla.mozilla.org/show_bug.cgi?id=1396758
+    if (isOnRemoved && tabId && tabs.map((t) => { return t.id; }).includes(tabId)) {
+      length--;
+    }
+
+    browser.browserAction.setBadgeText({text: length.toString()});
+    if (length > 2) {
+      browser.browserAction.setBadgeBackgroundColor({'color': 'green'});
+    } else {
+      browser.browserAction.setBadgeBackgroundColor({'color': 'red'});
+    }
+  });
+}
+
+
+browser.tabs.onRemoved.addListener(
+  (tabId) => { updateCount(tabId, true);
+});
+browser.tabs.onCreated.addListener(
+  (tabId) => { updateCount(tabId, false);
+});
+updateCount();
diff --git a/tabs-tabs-tabs/manifest.json b/tabs-tabs-tabs/manifest.json
index 76663af..6159095 100644
--- a/tabs-tabs-tabs/manifest.json
+++ b/tabs-tabs-tabs/manifest.json
@@ -1,4 +1,7 @@
 {
+  "background": {
+      "scripts": ["background.js"]
+  },
   "browser_action": {
     "browser_style": true,
     "default_title": "Tabs, tabs, tabs",