diff --git a/js/src/frontend/Parser.cpp b/js/src/frontend/Parser.cpp
index 4cdc38594241..7b716267fdfd 100644
--- a/js/src/frontend/Parser.cpp
+++ b/js/src/frontend/Parser.cpp
@@ -449,6 +449,8 @@ Parser<ParseHandler>::Parser(ExclusiveContext *cx, LifoAlloc *alloc,
 template <typename ParseHandler>
 Parser<ParseHandler>::~Parser()
 {
+    accumulateTelemetry();
+
     alloc.release(tempPoolMark);
 
     /*
@@ -7567,6 +7569,29 @@ Parser<ParseHandler>::exprInParens()
     return pn;
 }
 
+template <typename ParseHandler>
+void
+Parser<ParseHandler>::accumulateTelemetry()
+{
+    JSContext* cx = context->maybeJSContext();
+    if (!cx)
+        return;
+    JSAccumulateTelemetryDataCallback cb = cx->runtime()->telemetryCallback;
+    if (!cb)
+        return;
+    const char* filename = getFilename();
+    if (!filename)
+        return;
+
+    bool isHTTP = strncmp(filename, "http://", 7) == 0 || strncmp(filename, "https://", 8) == 0;
+
+    // Only report telemetry for web content, not add-ons or chrome JS.
+    if (!isHTTP)
+        return;
+
+    // TODO: Call back into Firefox's Telemetry reporter.
+}
+
 template class Parser<FullParseHandler>;
 template class Parser<SyntaxParseHandler>;
 
diff --git a/js/src/frontend/Parser.h b/js/src/frontend/Parser.h
index fb1f759a14d4..ba4272741b44 100644
--- a/js/src/frontend/Parser.h
+++ b/js/src/frontend/Parser.h
@@ -658,6 +658,8 @@ class Parser : private JS::AutoGCRooter, public StrictModeGetter
 
     bool asmJS(Node list);
 
+    void accumulateTelemetry();
+
     friend class LegacyCompExprTransplanter;
     friend struct BindData<ParseHandler>;
 };
diff --git a/js/src/jsfriendapi.h b/js/src/jsfriendapi.h
index e175b33b403e..547dea6706c1 100644
--- a/js/src/jsfriendapi.h
+++ b/js/src/jsfriendapi.h
@@ -119,7 +119,8 @@ enum {
     JS_TELEMETRY_GC_INCREMENTAL_DISABLED,
     JS_TELEMETRY_GC_NON_INCREMENTAL,
     JS_TELEMETRY_GC_SCC_SWEEP_TOTAL_MS,
-    JS_TELEMETRY_GC_SCC_SWEEP_MAX_PAUSE_MS
+    JS_TELEMETRY_GC_SCC_SWEEP_MAX_PAUSE_MS,
+    JS_TELEMETRY_DEPRECATED_LANGUAGE_EXTENSIONS_IN_CONTENT
 };
 
 typedef void
diff --git a/js/xpconnect/src/XPCJSRuntime.cpp b/js/xpconnect/src/XPCJSRuntime.cpp
index 3532c4c05a61..5514bf25f09a 100644
--- a/js/xpconnect/src/XPCJSRuntime.cpp
+++ b/js/xpconnect/src/XPCJSRuntime.cpp
@@ -2929,6 +2929,11 @@ AccumulateTelemetryCallback(int id, uint32_t sample)
       case JS_TELEMETRY_GC_SCC_SWEEP_MAX_PAUSE_MS:
         Telemetry::Accumulate(Telemetry::GC_SCC_SWEEP_MAX_PAUSE_MS, sample);
         break;
+      case JS_TELEMETRY_DEPRECATED_LANGUAGE_EXTENSIONS_IN_CONTENT:
+        Telemetry::Accumulate(Telemetry::JS_DEPRECATED_LANGUAGE_EXTENSIONS_IN_CONTENT, sample);
+        break;
+      default:
+        MOZ_ASSERT_UNREACHABLE("Unexpected JS_TELEMETRY id");
     }
 }
 
diff --git a/toolkit/components/telemetry/Histograms.json b/toolkit/components/telemetry/Histograms.json
index 7037df4e4522..a916830ace28 100644
--- a/toolkit/components/telemetry/Histograms.json
+++ b/toolkit/components/telemetry/Histograms.json
@@ -318,6 +318,12 @@
     "kind": "flag",
     "description": "Has seen location error"
   },
+  "JS_DEPRECATED_LANGUAGE_EXTENSIONS_IN_CONTENT": {
+    "expires_in_version": "never",
+    "kind": "enumerated",
+    "n_values": 10,
+    "description": "Use of SpiderMonkey's deprecated language extensions in web content"
+  },
   "TELEMETRY_PING": {
     "expires_in_version": "never",
     "kind": "exponential",