--- a/netwerk/protocol/http/nsHttpChannel.cpp
+++ b/netwerk/protocol/http/nsHttpChannel.cpp
@@ -1451,53 +1451,52 @@ EnsureMIMEOfScript(nsIURI* aURI, nsHttpR
     }
 
     if (aLoadInfo->GetExternalContentPolicyType() != nsIContentPolicy::TYPE_SCRIPT) {
         // if this is not a script load, then there is nothing to do
         return NS_OK;
     }
 
     nsAutoCString contentType;
-    nsCOMPtr<nsIURI> requestURI;
-    nsAutoCString requestURIString;
-    nsAutoCString responseURIString;
-    nsAutoCString corsOrigin;
 
     aResponseHead->ContentType(contentType);
     NS_ConvertUTF8toUTF16 typeString(contentType);
 
     if (nsContentUtils::IsJavascriptMIMEType(typeString)) {
         // script load has type script
         AccumulateCategorical(Telemetry::LABELS_SCRIPT_BLOCK_INCORRECT_MIME_2::javaScript);
         return NS_OK;
     }
 
-    if (aLoadInfo->LoadingPrincipal()) {
-        aLoadInfo->LoadingPrincipal()->GetURI(getter_AddRefs(requestURI));
-        if (requestURI) {
-            requestURI->GetPrePath(requestURIString);
-        }
-        aURI->GetPrePath(responseURIString);
-        if (requestURIString.Equals(responseURIString)) {
-            //same origin
-            AccumulateCategorical(Telemetry::LABELS_SCRIPT_BLOCK_INCORRECT_MIME_2::same_origin);
-        } else {
-            bool cors = false;
-            nsresult rv = aResponseHead->GetHeader(nsHttp::ResolveAtom("Access-Control-Allow-Origin"), corsOrigin);
-            if (NS_SUCCEEDED(rv)) {
-                //cors origin
-                if (corsOrigin.Equals("*") || corsOrigin.Equals(requestURIString)) {
-                    AccumulateCategorical(Telemetry::LABELS_SCRIPT_BLOCK_INCORRECT_MIME_2::CORS_same_origin);
-                    cors = true;
-                }
+    nsCOMPtr<nsIURI> requestURI;
+    nsAutoCString requestURIString;
+    aLoadInfo->TriggeringPrincipal()->GetURI(getter_AddRefs(requestURI));
+    if (requestURI) {
+        requestURI->GetPrePath(requestURIString);
+    }
+
+    nsIScriptSecurityManager* ssm = nsContentUtils::GetSecurityManager();
+    nsresult rv = ssm->CheckSameOriginURI(requestURI, aURI, false);
+    if (NS_SUCCEEDED(rv)) {
+        //same origin
+        AccumulateCategorical(Telemetry::LABELS_SCRIPT_BLOCK_INCORRECT_MIME_2::same_origin);
+    } else {
+        bool cors = false;
+        nsAutoCString corsOrigin;
+        rv = aResponseHead->GetHeader(nsHttp::ResolveAtom("Access-Control-Allow-Origin"), corsOrigin);
+        if (NS_SUCCEEDED(rv)) {
+            //cors origin
+            if (corsOrigin.Equals("*") || corsOrigin.Equals(requestURIString)) {
+                AccumulateCategorical(Telemetry::LABELS_SCRIPT_BLOCK_INCORRECT_MIME_2::CORS_origin);
+                cors = true;
             }
-            if (!cors) {
-                //cross origin
-                AccumulateCategorical(Telemetry::LABELS_SCRIPT_BLOCK_INCORRECT_MIME_2::cross_origin);
-            }
+        }
+        if (!cors) {
+            //cross origin
+            AccumulateCategorical(Telemetry::LABELS_SCRIPT_BLOCK_INCORRECT_MIME_2::cross_origin);
         }
     }
 
     bool block = false;
     if (StringBeginsWith(contentType, NS_LITERAL_CSTRING("image/"))) {
         // script load has type image
         AccumulateCategorical(Telemetry::LABELS_SCRIPT_BLOCK_INCORRECT_MIME_2::image);
         block = true;

--- a/toolkit/components/telemetry/Histograms.json
+++ b/toolkit/components/telemetry/Histograms.json
@@ -7798,18 +7798,18 @@
     "description": "Whether the user is in safe mode (No, Yes, Forced)"
   },
   "SCRIPT_BLOCK_INCORRECT_MIME_2": {
     "record_in_processes": ["main", "content"],
     "alert_emails": ["ckerschbaumer@mozilla.com"],
     "bug_numbers": [1288361, 1299267, 1399990],
     "expires_in_version": "63",
     "kind": "categorical",
-    "labels": ["unknown","javaScript","image", "audio", "video","text_plain","text_csv","text_xml","app_octet_stream","app_xml","text_html","empty","worker_load","importSript_load","script_load","same_origin","CORS_same_origin","cross_origin"],
-    "description": "Whether the script load has a MIME type of ...?  (unknown, javaScript, image, audio, video, text_plain, text_csv, text_xml, app_octet_stream, app_xml, text_html, empty). Whether the script load is from ...?  (worker_load, importSript_load, script_load). Whether the script load is of ...?  (same_origin, CORS_same_origin, cross_origin)"
+    "labels": ["unknown","javaScript","image", "audio", "video","text_plain","text_csv","text_xml","app_octet_stream","app_xml","text_html","empty","worker_load","importSript_load","script_load","same_origin","CORS_origin","cross_origin"],
+    "description": "Whether the script load has a MIME type of ...?  (unknown, javaScript, image, audio, video, text_plain, text_csv, text_xml, app_octet_stream, app_xml, text_html, empty). Whether the script load is from ...?  (worker_load, importSript_load, script_load). Whether the script load is of ...?  (same_origin, CORS_origin, cross_origin)"
   },
   "XCTO_NOSNIFF_BLOCK_IMAGE": {
     "record_in_processes": ["main", "content"],
     "alert_emails": ["ckerschbaumer@mozilla.com"],
     "bug_numbers": [1302539],
     "expires_in_version": "56",
     "kind": "enumerated",
     "n_values": 3,