--- a/js/src/asmjs/WasmBinary.h
+++ b/js/src/asmjs/WasmBinary.h
@@ -19,16 +19,24 @@
 #ifndef wasm_binary_h
 #define wasm_binary_h
 
 #include "builtin/SIMD.h"
 
 namespace js {
 namespace wasm {
 
+// Telemetry sample values for the JS_AOT_USAGE key, indicating whether asm.js
+// or WebAssembly is used.
+
+enum class Telemetry {
+    ASMJS = 0,
+    WASM = 1
+};
+
 static const uint32_t MagicNumber        = 0x6d736100; // "\0asm"
 static const uint32_t EncodingVersion    = 0x0b;
 
 static const char TypeSectionId[]        = "type";
 static const char GlobalSectionId[]      = "global";
 static const char ImportSectionId[]      = "import";
 static const char FunctionSectionId[]    = "function";
 static const char TableSectionId[]       = "table";

--- a/js/src/asmjs/WasmModule.cpp
+++ b/js/src/asmjs/WasmModule.cpp
@@ -865,10 +865,13 @@ Module::instantiate(JSContext* cx,
                 return false;
         } else {
             uint32_t funcDefIndex = startFuncIndex - funcImports.length();
             if (!instance->instance().callExport(cx, funcDefIndex, args))
                 return false;
         }
     }
 
+    uint32_t mode = uint32_t(metadata().isAsmJS() ? Telemetry::ASMJS : Telemetry::WASM);
+    cx->runtime()->addTelemetry(JS_TELEMETRY_AOT_USAGE, mode);
+
     return true;
 }

--- a/js/src/jsfriendapi.h
+++ b/js/src/jsfriendapi.h
@@ -128,16 +128,17 @@ enum {
     JS_TELEMETRY_GC_MINOR_REASON,
     JS_TELEMETRY_GC_MINOR_REASON_LONG,
     JS_TELEMETRY_GC_MINOR_US,
     JS_TELEMETRY_GC_NURSERY_BYTES,
     JS_TELEMETRY_GC_PRETENURE_COUNT,
     JS_TELEMETRY_DEPRECATED_LANGUAGE_EXTENSIONS_IN_CONTENT,
     JS_TELEMETRY_DEPRECATED_LANGUAGE_EXTENSIONS_IN_ADDONS,
     JS_TELEMETRY_ADDON_EXCEPTIONS,
+    JS_TELEMETRY_AOT_USAGE,
     JS_TELEMETRY_END
 };
 
 typedef void
 (*JSAccumulateTelemetryDataCallback)(int id, uint32_t sample, const char* key);
 
 extern JS_FRIEND_API(void)
 JS_SetAccumulateTelemetryCallback(JSContext* cx, JSAccumulateTelemetryDataCallback callback);

--- a/js/xpconnect/src/XPCJSRuntime.cpp
+++ b/js/xpconnect/src/XPCJSRuntime.cpp
@@ -3154,16 +3154,19 @@ AccumulateTelemetryCallback(int id, uint
         Telemetry::Accumulate(Telemetry::JS_DEPRECATED_LANGUAGE_EXTENSIONS_IN_CONTENT, sample);
         break;
       case JS_TELEMETRY_DEPRECATED_LANGUAGE_EXTENSIONS_IN_ADDONS:
         Telemetry::Accumulate(Telemetry::JS_DEPRECATED_LANGUAGE_EXTENSIONS_IN_ADDONS, sample);
         break;
       case JS_TELEMETRY_ADDON_EXCEPTIONS:
         Telemetry::Accumulate(Telemetry::JS_TELEMETRY_ADDON_EXCEPTIONS, nsDependentCString(key), sample);
         break;
+      case JS_TELEMETRY_AOT_USAGE:
+        Telemetry::Accumulate(Telemetry::JS_AOT_USAGE, sample);
+        break;
       default:
         MOZ_ASSERT_UNREACHABLE("Unexpected JS_TELEMETRY id");
     }
 }
 
 static void
 CompartmentNameCallback(JSContext* cx, JSCompartment* comp,
                         char* buf, size_t bufsize)

--- a/toolkit/components/telemetry/Histograms.json
+++ b/toolkit/components/telemetry/Histograms.json
@@ -10294,10 +10294,18 @@
   "WEB_PERMISSION_CLEARED": {
     "alert_emails": ["firefox-dev@mozilla.org"],
     "bug_numbers": [1286118],
     "expires_in_version": "55",
     "kind": "enumerated",
     "keyed": true,
     "n_values": 6,
     "description": "Number of revoke actions on permissions in the control center, keyed by permission id. Values represent the permission type that was revoked. (0=unknown, 1=permanently allowed, 2=permanently blocked, 3=temporarily allowed, 4=temporarily blocked)"
+  },
+  "JS_AOT_USAGE": {
+    "alert_emails": ["luke@mozilla.com", "bbouvier@mozilla.com"],
+    "bug_numbers": [1288778],
+    "expires_in_version": "56",
+    "kind": "enumerated",
+    "n_values": 4,
+    "description": "Counts the number of asm.js vs WebAssembly modules instanciations, at the time modules are getting instanciated."
   }
 }