diff --git a/platform/firefox/vapi-client.js b/platform/firefox/vapi-client.js
index abbc59957..7a8a716d4 100644
--- a/platform/firefox/vapi-client.js
+++ b/platform/firefox/vapi-client.js
@@ -81,8 +81,9 @@ vAPI.shutdown = (function() {
     }
     var filters = self.rpc({
         fnName: 'getScriptTagFilters',
-        url: location.href,
-        hostname: hostname
+        rootURL: self.top.location.href,
+        frameURL: self.location.href,
+        frameHostname: hostname
     });
     if ( typeof filters !== 'string' || filters === '' ) {
         return;
diff --git a/src/js/rpcreceiver.js b/src/js/rpcreceiver.js
index 995fd76ff..48d1068ff 100644
--- a/src/js/rpcreceiver.js
+++ b/src/js/rpcreceiver.js
@@ -38,12 +38,21 @@ if ( typeof vAPI.rpcReceiver !== 'object' ) {
 vAPI.rpcReceiver.getScriptTagFilters = function(details) {
     var µb = µBlock;
     var cfe = µb.cosmeticFilteringEngine;
-    if ( !cfe ) { return; }
-    var hostname = details.hostname;
-    return cfe.retrieveScriptTagRegex(
+    if ( !cfe ) {
+        return;
+    }
+    // Fetching the script tag filters first: assuming it is faster than
+    // checking whether the site is whitelisted.
+    var hostname = details.frameHostname;
+    var r = cfe.retrieveScriptTagRegex(
         µb.URI.domainFromHostname(hostname) || hostname,
         hostname
     );
+    // https://github.com/gorhill/uBlock/issues/838
+    // Disable script tag filtering if document URL is whitelisted.
+    if ( r !== undefined && µb.getNetFilteringSwitch(details.rootURL) ) {
+        return r;
+    }
 };
 
 /******************************************************************************/