--- a/toolkit/components/telemetry/TelemetryHistograms.h
+++ b/toolkit/components/telemetry/TelemetryHistograms.h
@@ -46,16 +46,17 @@
  * The other data reported by telemetry is listed on https://wiki.mozilla.org/Privacy/Reviews/Telemetry/Measurements
  *
  */
 
 /**
  * a11y telemetry
  */
 HISTOGRAM(A11Y_INSTANTIATED, 0, 1, 2, BOOLEAN, "has accessibility support been instantiated")
+HISTOGRAM(DLLBLOCKLIST_HOOK_INSTALLED, 0, 1, 2, BOOLEAN, "was the DLL blocklist hook installed successfully")
 
 HISTOGRAM(CYCLE_COLLECTOR, 1, 10000, 50, EXPONENTIAL, "Time spent on one cycle collection (ms)")
 HISTOGRAM(CYCLE_COLLECTOR_VISITED_REF_COUNTED, 1, 300000, 50, EXPONENTIAL, "Number of ref counted objects visited by the cycle collector")
 HISTOGRAM(CYCLE_COLLECTOR_VISITED_GCED, 1, 300000, 50, EXPONENTIAL, "Number of JS objects visited by the cycle collector")
 HISTOGRAM(CYCLE_COLLECTOR_COLLECTED, 1, 100000, 50, EXPONENTIAL, "Number of objects collected by the cycle collector")
 HISTOGRAM(TELEMETRY_PING, 1, 3000, 10, EXPONENTIAL, "Time taken to submit telemetry info (ms)")
 HISTOGRAM(TELEMETRY_SUCCESS, 0, 1, 2, BOOLEAN,  "Successful telemetry submission")
 HISTOGRAM(MEMORY_JS_COMPARTMENTS_SYSTEM, 1, 1000, 10, EXPONENTIAL, "Total JavaScript compartments used for add-ons and internals.")

--- a/toolkit/xre/nsWindowsDllBlocklist.cpp
+++ b/toolkit/xre/nsWindowsDllBlocklist.cpp
@@ -50,16 +50,20 @@
 
 #include "prlog.h"
 
 #include "nsWindowsDllInterceptor.h"
 
 #define IN_WINDOWS_DLL_BLOCKLIST
 #include "nsWindowsDllBlocklist.h"
 
+#include "mozilla/Telemetry.h"
+
+using namespace mozilla;
+
 #ifndef STATUS_DLL_NOT_FOUND
 #define STATUS_DLL_NOT_FOUND ((DWORD)0xC0000135L)
 #endif
 
 // define this for very verbose dll load debug spew
 #undef DEBUG_very_verbose
 
 typedef NTSTATUS (NTAPI *LdrLoadDll_func) (PWCHAR filePath, PULONG flags, PUNICODE_STRING moduleFileName, PHANDLE handle);
@@ -217,13 +221,14 @@ WindowsDllInterceptor NtDllIntercept;
 
 void
 XRE_SetupDllBlocklist()
 {
   NtDllIntercept.Init("ntdll.dll");
 
   bool ok = NtDllIntercept.AddHook("LdrLoadDll", reinterpret_cast<intptr_t>(patched_LdrLoadDll), (void**) &stub_LdrLoadDll);
 
+  Telemetry::Accumulate(Telemetry::DLLBLOCKLIST_HOOK_INSTALLED, ok ? 1 : 0);
 #ifdef DEBUG
   if (!ok)
     printf_stderr ("LdrLoadDll hook failed, no dll blocklisting active\n");
 #endif
 }