--- a/toolkit/components/telemetry/Histograms.json
+++ b/toolkit/components/telemetry/Histograms.json
@@ -4018,16 +4018,27 @@
   "HTTPCONNMGR_UNUSED_SPECULATIVE_CONN": {
     "record_in_processes": ["main", "content"],
     "expires_in_version": "never",
     "kind": "exponential",
     "high": 1000000,
     "n_buckets": 50,
     "description": "How many speculative connections are made needlessly"
   },
+  "TAB_COUNT": {
+    "record_in_processes": ["main", "content"],
+    "alert_emails": [],
+    "bug_numbers": [1361855],
+    "expires_in_version": "60",
+    "kind": "exponential",
+    "high": 1000,
+    "n_buckets": 100,
+    "releaseChannelCollection": "opt-out",
+    "description": "Number of tabs opened across all windows, collected at most every 5 minutes whenever the user interacts with the browser in the following ways: open tab/window, page load."
+  },
   "TAP_TO_LOAD_IMAGE_SIZE": {
     "record_in_processes": ["main", "content"],
     "expires_in_version": "50",
     "kind": "exponential",
     "high": 32768,
     "n_buckets": 50,
     "description": "The size of the image being shown, when using tap-to-load images. (kilobytes)",
     "bug_numbers": [1208167]