diff --git a/src/js/httpheader-filtering.js b/src/js/httpheader-filtering.js
new file mode 100644
index 000000000..52e78721a
--- /dev/null
+++ b/src/js/httpheader-filtering.js
@@ -0,0 +1,228 @@
+/*******************************************************************************
+
+    uBlock Origin - a browser extension to block requests.
+    Copyright (C) 2021-present Raymond Hill
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see {http://www.gnu.org/licenses/}.
+
+    Home: https://github.com/gorhill/uBlock
+*/
+
+'use strict';
+
+/******************************************************************************/
+
+{
+// >>>>> start of local scope
+
+/******************************************************************************/
+
+const µb = µBlock;
+const duplicates = new Set();
+const filterDB = new µb.staticExtFilteringEngine.HostnameBasedDB(1);
+const sessionFilterDB = new µb.staticExtFilteringEngine.SessionDB();
+
+const $headers = new Set();
+const $exceptions = new Set();
+
+let acceptedCount = 0;
+let discardedCount = 0;
+
+const headerIndexFromName = function(name, headers) {
+    let i = headers.length;
+    while ( i-- ) {
+        if ( headers[i].name.toLowerCase() === name ) {
+            return i;
+        }
+    }
+    return -1;
+};
+
+const logOne = function(isException, token, fctxt) {
+    fctxt.duplicate()
+        .setRealm('extended')
+        .setType('header')
+        .setFilter({
+            modifier: true,
+            result: isException ? 2 : 1,
+            source: 'extended',
+            raw: `${(isException ? '#@#' : '##')}^responseheader(${token})`
+        })
+        .toLogger();
+};
+
+const api = {
+    get acceptedCount() {
+        return acceptedCount;
+    },
+    get discardedCount() {
+        return discardedCount;
+    }
+};
+
+api.reset = function() {
+    filterDB.clear();
+    duplicates.clear();
+    acceptedCount = 0;
+    discardedCount = 0;
+};
+
+api.freeze = function() {
+    duplicates.clear();
+    filterDB.collectGarbage();
+};
+
+api.compile = function(parser, writer) {
+    writer.select(µb.compiledHTTPHeaderSection);
+
+    const { compiled, exception } = parser.result;
+    const headerName = compiled.slice(15, -1);
+
+    // Tokenless is meaningful only for exception filters.
+    if ( headerName === '' && exception === false ) { return; }
+
+    // Only exception filters are allowed to be global.
+    if ( parser.hasOptions() === false ) {
+        if ( exception ) {
+            writer.push([ 64, '', 1, compiled ]);
+        }
+        return;
+    }
+
+    // https://github.com/gorhill/uBlock/issues/3375
+    //   Ignore instances of exception filter with negated hostnames,
+    //   because there is no way to create an exception to an exception.
+
+    for ( const { hn, not, bad } of parser.extOptions() ) {
+        if ( bad ) { continue; }
+        let kind = 0;
+        if ( exception ) {
+            if ( not ) { continue; }
+            kind |= 1;
+        } else if ( not ) {
+            kind |= 1;
+        }
+        writer.push([ 64, hn, kind, compiled ]);
+    }
+};
+
+api.compileTemporary = function(parser) {
+    return {
+        session: sessionFilterDB,
+        selector: parser.result.compiled.slice(15, -1),
+    };
+};
+
+// 01234567890123456789
+// responseheader(name)
+//                ^   ^
+//               15  -1
+
+api.fromCompiledContent = function(reader) {
+    reader.select(µb.compiledHTTPHeaderSection);
+
+    while ( reader.next() ) {
+        acceptedCount += 1;
+        const fingerprint = reader.fingerprint();
+        if ( duplicates.has(fingerprint) ) {
+            discardedCount += 1;
+            continue;
+        }
+        duplicates.add(fingerprint);
+        const args = reader.args();
+        if ( args.length < 4 ) { continue; }
+        filterDB.store(args[1], args[2], args[3].slice(15, -1));
+    }
+};
+
+api.getSession = function() {
+    return sessionFilterDB;
+};
+
+api.apply = function(fctxt, headers) {
+    if ( filterDB.size === 0 ) { return; }
+
+    const hostname = fctxt.getHostname();
+    if ( hostname === '' ) { return; }
+
+    const domain = fctxt.getDomain();
+    let entity = µb.URI.entityFromDomain(domain);
+    if ( entity !== '' ) {
+        entity = `${hostname.slice(0, -domain.length)}${entity}`;
+    } else {
+        entity = '*';
+    }
+
+    $headers.clear();
+    $exceptions.clear();
+
+    if ( sessionFilterDB.isNotEmpty ) {
+        sessionFilterDB.retrieve([ null, $exceptions ]);
+    }
+    filterDB.retrieve(hostname, [ $headers, $exceptions ]);
+    filterDB.retrieve(entity, [ $headers, $exceptions ], 1);
+    if ( $headers.size === 0 ) { return; }
+
+    // https://github.com/gorhill/uBlock/issues/2835
+    //   Do not filter response headers if the site is under an `allow` rule.
+    if (
+        µb.userSettings.advancedUserEnabled &&
+        µb.sessionFirewall.evaluateCellZY(hostname, hostname, '*') === 2
+    ) {
+        return;
+    }
+
+    const hasGlobalException = $exceptions.has('');
+    const loggerEnabled = µb.logger.enabled;
+
+    let modified = false;
+
+    for ( const name of $headers ) {
+        for (;;) {
+            const i = headerIndexFromName(name, headers);
+            if ( i === -1 ) { break; }
+            const isExcepted = hasGlobalException || $exceptions.has(name);
+            if ( isExcepted ) {
+                if ( loggerEnabled ) {
+                    logOne(true, hasGlobalException ? '' : name, fctxt);
+                }
+                break;
+            }
+            headers.splice(i, 1);
+            if ( loggerEnabled ) {
+                logOne(false, name, fctxt);
+            }
+            modified = true;
+        }
+    }
+
+    return modified;
+};
+
+api.toSelfie = function() {
+    return filterDB.toSelfie();
+};
+
+api.fromSelfie = function(selfie) {
+    filterDB.fromSelfie(selfie);
+};
+
+µb.httpheaderFilteringEngine = api;
+
+/******************************************************************************/
+
+// <<<<< end of local scope
+}
+
+/******************************************************************************/