diff --git a/platform/firefox/frameModule.js b/platform/firefox/frameModule.js
index d01309a7d..ebb6378f0 100644
--- a/platform/firefox/frameModule.js
+++ b/platform/firefox/frameModule.js
@@ -248,26 +248,27 @@ var contentObserver = {
             return this.ACCEPT;
         }
 
-        let details = {
-            frameId: this.getFrameId(context),
-            parentFrameId: context.parent === context.top ? 0 : this.getFrameId(context.parent),
-            rawtype: type,
-            tabId: '',
-            url: location.spec
-        };
+        let rpcData = this.rpcData;
+        rpcData.frameId = this.getFrameId(context);
+        rpcData.pFrameId = context.parent === context.top ? 0 : this.getFrameId(context.parent);
+        rpcData.type = type;
+        rpcData.url = location.spec;
 
         //console.log('shouldLoad: type=' + type + ' url=' + location.spec);
         if ( typeof messageManager.sendRpcMessage === 'function' ) {
             // https://bugzil.la/1092216
-            messageManager.sendRpcMessage(this.cpMessageName, details);
+            messageManager.sendRpcMessage(this.cpMessageName, rpcData);
         } else {
             // Compatibility for older versions
-            messageManager.sendSyncMessage(this.cpMessageName, details);
+            messageManager.sendSyncMessage(this.cpMessageName, rpcData);
         }
 
         return this.ACCEPT;
     },
 
+    // Reuse object to avoid repeated memory allocation.
+    rpcData: { frameId: 0, pFrameId: -1, type: 0, url: '' },
+
     initContentScripts: function(win, create) {
         let messager = getMessageManager(win);
         let sandboxId = hostName + ':sb:' + this.uniqueSandboxId++;
diff --git a/platform/firefox/vapi-background.js b/platform/firefox/vapi-background.js
index 108ad61e3..324651d97 100644
--- a/platform/firefox/vapi-background.js
+++ b/platform/firefox/vapi-background.js
@@ -2089,19 +2089,7 @@ var httpObserver = {
     },
 
     // https://github.com/gorhill/uBlock/issues/959
-    //   Try to synthesize a pending request from a behind-the-scene request.
-    synthesizePendingRequest: function(channel, rawtype) {
-        var tabId = this.tabIdFromChannel(channel);
-        if ( tabId === vAPI.noTabId ) {
-            return null;
-        }
-        return {
-            frameId: 0,
-            parentFrameId: -1,
-            tabId: tabId,
-            rawtype: rawtype
-        };
-    },
+    syntheticPendingRequest: { frameId: 0, parentFrameId: -1, tabId: '', rawtype: 1 },
 
     handleRequest: function(channel, URI, details) {
         var type = this.typeMap[details.rawtype] || 'other';
@@ -2244,37 +2232,28 @@ var httpObserver = {
             }
         }
 
-        // IMPORTANT:
-        // If this is a main frame, ensure that the proper tab id is being
-        // used: it can happen that the wrong tab id was looked up at
-        // `shouldLoadListener` time. Without this, the popup blocker may
-        // not work properly, and also a tab opened from a link may end up
-        // being wrongly reported as an embedded element.
-        if ( pendingRequest !== null && pendingRequest.rawtype === 6 ) {
-            var tabId = this.tabIdFromChannel(channel);
-            if ( tabId !== vAPI.noTabId ) {
-                pendingRequest.tabId = tabId;
+        if ( pendingRequest !== null ) {
+            // https://github.com/gorhill/uBlock/issues/654
+            //   Use the request type from the HTTP observer point of view.
+            if ( rawtype !== 1 ) {
+                pendingRequest.rawtype = rawtype;
             }
-        }
-
-        // Behind-the-scene request... Really?
-        if ( pendingRequest === null ) {
-            pendingRequest = this.synthesizePendingRequest(channel, rawtype);
-        }
-
-        // Behind-the-scene request... Yes, really.
-        if ( pendingRequest === null ) {
-            pendingRequest = {
-                frameId: 0,
-                parentFrameId: -1,
-                tabId: vAPI.noTabId,
-                rawtype: rawtype
-            };
-        }
-
-        // https://github.com/gorhill/uBlock/issues/654
-        // Use the request type from the HTTP observer point of view.
-        if ( rawtype !== 1 ) {
+            // IMPORTANT:
+            // If this is a main frame, ensure that the proper tab id is being
+            // used: it can happen that the wrong tab id was looked up at
+            // `shouldLoadListener` time. Without this, the popup blocker may
+            // not work properly, and also a tab opened from a link may end up
+            // being wrongly reported as an embedded element.
+            if ( pendingRequest.rawtype === 6 ) {
+                var tabId = this.tabIdFromChannel(channel);
+                if ( tabId !== vAPI.noTabId ) {
+                    pendingRequest.tabId = tabId;
+                }
+            }
+        } else { // pendingRequest === null
+            // No matching pending request found, synthetize one.
+            pendingRequest = this.syntheticPendingRequest;
+            pendingRequest.tabId = this.tabIdFromChannel(channel);
             pendingRequest.rawtype = rawtype;
         }
 
@@ -2401,8 +2380,8 @@ vAPI.net.registerListeners = function() {
         // request into a ring buffer for later retrieval by the HTTP observer.
         var pendingReq = httpObserver.createPendingRequest(details.url);
         pendingReq.frameId = details.frameId;
-        pendingReq.parentFrameId = details.parentFrameId;
-        pendingReq.rawtype = details.rawtype;
+        pendingReq.parentFrameId = details.pFrameId;
+        pendingReq.rawtype = details.type;
         pendingReq.tabId = tabWatcher.tabIdFromTarget(e.target);
     };
 
diff --git a/src/js/contentscript.js b/src/js/contentscript.js
index ef65718e1..799f23091 100644
--- a/src/js/contentscript.js
+++ b/src/js/contentscript.js
@@ -1516,7 +1516,7 @@ vAPI.executionCost.stop('domIsLoaded');
 /******************************************************************************/
 
 if ( document.readyState !== 'loading' ) {
-    domIsLoaded();
+    window.requestAnimationFrame(domIsLoaded);
 } else {
     document.addEventListener('DOMContentLoaded', domIsLoaded);
 }