--- a/ipc/glue/MessageChannel.cpp
+++ b/ipc/glue/MessageChannel.cpp
@@ -1274,19 +1274,19 @@ MessageChannel::Send(Message* aMsg, Mess
     MOZ_RELEASE_ASSERT(reply->is_sync());
 
     *aReply = Move(*reply);
     if (aReply->size() >= kMinTelemetryMessageSize) {
         Telemetry::Accumulate(Telemetry::IPC_REPLY_SIZE,
                               nsDependentCString(msgName), aReply->size());
     }
 
-    // NOTE: Only collect IPC_SYNC_LATENCY_MS on the main thread (bug 1343729)
+    // NOTE: Only collect IPC_SYNC_MAIN_LATENCY_MS on the main thread (bug 1343729)
     if (NS_IsMainThread() && latencyMs >= kMinTelemetrySyncIPCLatencyMs) {
-      Telemetry::Accumulate(Telemetry::IPC_SYNC_LATENCY_MS,
+      Telemetry::Accumulate(Telemetry::IPC_SYNC_MAIN_LATENCY_MS,
                             nsDependentCString(msgName), latencyMs);
     }
     return true;
 }
 
 bool
 MessageChannel::Call(Message* aMsg, Message* aReply)
 {

--- a/toolkit/components/telemetry/Histograms.json
+++ b/toolkit/components/telemetry/Histograms.json
@@ -10623,25 +10623,26 @@
     "bug_numbers": [1264820],
     "expires_in_version": "55",
     "kind": "exponential",
     "high": 8000000,
     "n_buckets": 50,
     "keyed": true,
     "description": "Measures the size of IPC messages by message name"
   },
-  "IPC_SYNC_LATENCY_MS": {
+  "IPC_SYNC_MAIN_LATENCY_MS": {
     "alert_emails": ["cpearce@mozilla.com"],
     "bug_numbers": [1333489],
     "expires_in_version": "60",
     "kind": "exponential",
-    "high": 2000,
-    "n_buckets": 10,
-    "keyed": true,
-    "description": "Measures the number of milliseconds we spend waiting for sync IPC messages to finish sending, keyed by message name. Note: only messages that wait for more than 500 microseconds are included in this probe."
+    "low": 32,
+    "high": 750,
+    "n_buckets": 40,
+    "keyed": true,
+    "description": "Measures the number of milliseconds we spend waiting for sync IPC messages to finish sending, keyed by message name. Note: only messages that wait for more than 500 microseconds and block the main thread are included in this probe."
   },
   "MESSAGE_MANAGER_MESSAGE_SIZE2": {
     "alert_emails": ["wmccloskey@mozilla.com","amccreight@mozilla.com"],
     "bug_numbers": [1260908],
     "expires_in_version": "55",
     "kind": "exponential",
     "low": 8192,
     "high": 8000000,