diff --git a/platform/chromium/vapi-background.js b/platform/chromium/vapi-background.js
index 34e8d1c1218e9..770d27b355f91 100644
--- a/platform/chromium/vapi-background.js
+++ b/platform/chromium/vapi-background.js
@@ -655,8 +655,8 @@ vAPI.messaging.listen = function(listenerName, callback) {
 /******************************************************************************/
 
 vAPI.messaging.onPortMessage = (function() {
-    var messaging = vAPI.messaging;
-    var toAuxPending = {};
+    var messaging = vAPI.messaging,
+        toAuxPending = {};
 
     // Use a wrapper to avoid closure and to allow reuse.
     var CallbackWrapper = function(port, request, timeout) {
@@ -703,8 +703,8 @@ vAPI.messaging.onPortMessage = (function() {
     };
 
     var toAux = function(details, portFrom) {
-        var port, portTo;
-        var chromiumTabId = toChromiumTabId(details.toTabId);
+        var port, portTo,
+            chromiumTabId = toChromiumTabId(details.toTabId);
 
         // TODO: This could be an issue with a lot of tabs: easy to address
         //       with a port name to tab id map.
@@ -761,6 +761,32 @@ vAPI.messaging.onPortMessage = (function() {
         wrapper.callback(details.msg);
     };
 
+    var toFramework = function(msg, sender) {
+        var tabId = sender && sender.tab && sender.tab.id;
+        if ( !tabId ) { return; }
+        switch ( msg.what ) {
+        case 'userCSS':
+            if ( msg.toRemove ) {
+                chrome.tabs.removeCSS(tabId, {
+                    code: msg.toRemove,
+                    cssOrigin: 'user',
+                    frameId: sender.frameId,
+                    matchAboutBlank: true
+                });
+            }
+            if ( msg.toAdd ) {
+                chrome.tabs.insertCSS(tabId, {
+                    code: msg.toAdd,
+                    cssOrigin: 'user',
+                    frameId: sender.frameId,
+                    matchAboutBlank: true,
+                    runAt: 'document_start'
+                });
+            }
+            break;
+        }
+    };
+
     return function(request, port) {
         // Auxiliary process to auxiliary process
         if ( request.toTabId !== undefined ) {
@@ -774,6 +800,13 @@ vAPI.messaging.onPortMessage = (function() {
             return;
         }
 
+        // Content process to main process: framework handler.
+        // No callback supported/needed for now.
+        if ( request.channelName === 'vapi-background' ) {
+            toFramework(request.msg, port.sender);
+            return;
+        }
+
         // Auxiliary process to main process: prepare response
         var callback = messaging.NOOPFUNC;
         if ( request.auxProcessId !== undefined ) {
@@ -781,8 +814,8 @@ vAPI.messaging.onPortMessage = (function() {
         }
 
         // Auxiliary process to main process: specific handler
-        var r = messaging.UNHANDLED;
-        var listener = messaging.listeners[request.channelName];
+        var r = messaging.UNHANDLED,
+            listener = messaging.listeners[request.channelName];
         if ( typeof listener === 'function' ) {
             r = listener(request.msg, port.sender, callback);
         }
diff --git a/platform/webext/manifest.json b/platform/webext/manifest.json
index 5e77bef90ac5b..772e430c341c0 100644
--- a/platform/webext/manifest.json
+++ b/platform/webext/manifest.json
@@ -37,6 +37,7 @@
          ],
          "js":[
             "js/vapi-client.js",
+            "js/vapi-usercss.js",
             "js/contentscript.js"
          ],
          "run_at":"document_start",
diff --git a/platform/webext/vapi-usercss.js b/platform/webext/vapi-usercss.js
new file mode 100644
index 0000000000000..aea2a2bf501c8
--- /dev/null
+++ b/platform/webext/vapi-usercss.js
@@ -0,0 +1,77 @@
+/*******************************************************************************
+
+    uBlock Origin - a browser extension to block requests.
+    Copyright (C) 2017 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';
+
+// For content pages
+
+/******************************************************************************/
+
+(function() {
+    if ( typeof vAPI !== 'object' ) { return; }
+
+    vAPI.userCSS = {
+        _userCSS: '',
+        _disabled: false,
+        _send: function(toRemove, toAdd) {
+            vAPI.messaging.send('vapi-background', {
+                what: 'userCSS',
+                toRemove: toRemove,
+                toAdd: toAdd
+            });
+        },
+        add: function(cssText) {
+            if ( cssText === '' ) { return; }
+            var before = this._userCSS,
+                after = before;
+            if ( after !== '' ) { after += '\n'; }
+            after += cssText;
+            this._userCSS = after;
+            if ( this._disabled ) { return; }
+            this._send(before, after);
+        },
+        remove: function(cssText) {
+            if ( cssText === '' || this._userCSS === '' ) { return; }
+            var before = this._userCSS,
+                after = before;
+            after = before.replace(cssText, '').trim();
+            this._userCSS = after;
+            if ( this._disabled ) { return; }
+            this._send(before, after);
+        },
+        toggle: function(state) {
+            if ( state === undefined ) {
+                state = this._disabled;
+            }
+            if ( state !== this._disabled ) { return; }
+            this._disabled = !state;
+            if ( this._userCSS === '' ) { return; }
+            var toAdd, toRemove; 
+            if ( state ) {
+                toAdd = this._userCSS;
+            } else {
+                toRemove = this._userCSS;
+            }
+            this._send(toRemove, toAdd);
+        }
+    };
+    vAPI.hideNode = vAPI.unhideNode = function(){};
+})();
diff --git a/tools/make-webext.sh b/tools/make-webext.sh
index e9fda83149acf..2f64bf9268529 100755
--- a/tools/make-webext.sh
+++ b/tools/make-webext.sh
@@ -23,11 +23,12 @@ cp -R platform/chromium/img           $DES/webextension/
 cp platform/chromium/*.html           $DES/webextension/
 cp platform/chromium/*.json           $DES/webextension/
 cp platform/webext/polyfill.js        $DES/webextension/js/
+cp platform/webext/vapi-usercss.js    $DES/webextension/js/
+cp platform/webext/manifest.json      $DES/webextension/
 cp LICENSE.txt                        $DES/webextension/
                                   
 cp platform/webext/background.html    $DES/webextension/
 cp platform/webext/from-legacy.js     $DES/webextension/js/
-cp platform/webext/manifest.json      $DES/webextension/
 cp platform/webext/bootstrap.js       $DES/
 cp platform/webext/chrome.manifest    $DES/
 cp platform/webext/install.rdf        $DES/