--- a/toolkit/components/telemetry/Histograms.json
+++ b/toolkit/components/telemetry/Histograms.json
@@ -4115,16 +4115,25 @@
   "URLCLASSIFIER_LC_COMPLETIONS": {
     "alert_emails": ["safebrowsing-telemetry@mozilla.org"],
     "expires_in_version": "never",
     "kind": "exponential",
     "high": 200,
     "n_buckets": 10,
     "description": "Size of the completion cache in entries"
   },
+  "URLCLASSIFIER_UPDATE_REMOTE_NETWORK_ERROR": {
+    "alert_emails": ["safebrowsing-telemetry@mozilla.org"],
+    "expires_in_version": "60",
+    "kind": "enumerated",
+    "keyed": true,
+    "n_values": 30,
+    "bug_numbers": [1332780],
+    "description": "Network error from SafeBrowsing database updates. (0=sucess, 1=unknown error, 2=already connected, 3=not connected, 4=connection refused,5=net timeout, 6=offline, 7=port access not allowed, 8=net reset, 9=net interrupt, 10=proxy connection refused,11=partial transfer,12=inadequate security,13=unknown host,14=dns lookup queue full,15=unknown proxy host"
+  },
   "URLCLASSIFIER_UPDATE_REMOTE_STATUS2": {
     "alert_emails": ["safebrowsing-telemetry@mozilla.org"],
     "expires_in_version": "never",
     "kind": "enumerated",
     "keyed": true,
     "n_values": 16,
     "bug_numbers": [1311910],
     "description": "Server HTTP status code from SafeBrowsing database updates. (0=1xx, 1=200, 2=2xx, 3=204, 4=3xx, 5=400, 6=4xx, 7=403, 8=404, 9=408, 10=413, 11=5xx, 12=502|504|511, 13=503, 14=505, 15=Other). Keyed by provider"

--- a/toolkit/components/url-classifier/nsUrlClassifierStreamUpdater.cpp
+++ b/toolkit/components/url-classifier/nsUrlClassifierStreamUpdater.cpp
@@ -504,16 +504,42 @@ nsUrlClassifierStreamUpdater::AddRequest
   NS_ENSURE_SUCCESS(rv, rv);
 
   rv = httpChannel->SetRequestMethod(NS_LITERAL_CSTRING("POST"));
   NS_ENSURE_SUCCESS(rv, rv);
 
   return NS_OK;
 }
 
+// We might need to expand the bucket here if telemetry shows lots of errors
+// are neither connection errors nor DNS errors.
+static uint8_t NetworkErrorToBucket(nsresult rv)
+{
+  switch(rv) {
+  // Connection errors
+  case NS_ERROR_ALREADY_CONNECTED:        return 2;
+  case NS_ERROR_NOT_CONNECTED:            return 3;
+  case NS_ERROR_CONNECTION_REFUSED:       return 4;
+  case NS_ERROR_NET_TIMEOUT:              return 5;
+  case NS_ERROR_OFFLINE:                  return 6;
+  case NS_ERROR_PORT_ACCESS_NOT_ALLOWED:  return 7;
+  case NS_ERROR_NET_RESET:                return 8;
+  case NS_ERROR_NET_INTERRUPT:            return 9;
+  case NS_ERROR_PROXY_CONNECTION_REFUSED: return 10;
+  case NS_ERROR_NET_PARTIAL_TRANSFER:     return 11;
+  case NS_ERROR_NET_INADEQUATE_SECURITY:  return 12;
+  // DNS errors
+  case NS_ERROR_UNKNOWN_HOST:             return 13;
+  case NS_ERROR_DNS_LOOKUP_QUEUE_FULL:    return 14;
+  case NS_ERROR_UNKNOWN_PROXY_HOST:       return 15;
+  // Others
+  default:                                return 1;
+  }
+}
+
 // Map the HTTP response code to a Telemetry bucket
 static uint32_t HTTPStatusToBucket(uint32_t status)
 {
   uint32_t statusBucket;
   switch (status) {
   case 100:
   case 101:
     // Unexpected 1xx return code
@@ -644,22 +670,24 @@ nsUrlClassifierStreamUpdater::OnStartReq
       if (NS_SUCCEEDED(rv) && uri) {
         uri->GetAsciiSpec(spec);
       }
       LOG(("nsUrlClassifierStreamUpdater::OnStartRequest "
            "(status=%s, uri=%s, this=%p)", errorName.get(),
            spec.get(), this));
     }
 
+    uint8_t netErrCode = NS_FAILED(status) ? NetworkErrorToBucket(status) : 0;
+    mozilla::Telemetry::Accumulate(
+      mozilla::Telemetry::URLCLASSIFIER_UPDATE_REMOTE_NETWORK_ERROR,
+      mTelemetryProvider, netErrCode);
+
     if (NS_FAILED(status)) {
       // Assume we're overloading the server and trigger backoff.
       downloadError = true;
-      mozilla::Telemetry::Accumulate(mozilla::Telemetry::URLCLASSIFIER_UPDATE_REMOTE_STATUS2,
-                                     mTelemetryProvider, 15 /* unknown response code */);
-
     } else {
       bool succeeded = false;
       rv = httpChannel->GetRequestSucceeded(&succeeded);
       NS_ENSURE_SUCCESS(rv, rv);
 
       uint32_t requestStatus;
       rv = httpChannel->GetResponseStatus(&requestStatus);
       NS_ENSURE_SUCCESS(rv, rv);