Issue 5090 - Use user stylesheets for element hiding if possible

lib/css.js

Index: lib/css.js
diff --git a/lib/css.js b/lib/css.js
new file mode 100644
index 0000000000000000000000000000000000000000..f83daff86acc76b6b7e0a147e271243a945608e9
--- /dev/null
+++ b/lib/css.js
@@ -0,0 +1,54 @@
+/*
+ * This file is part of Adblock Plus <https://adblockplus.org/>,
+ * Copyright (C) 2006-2017 eyeo GmbH
+ *
+ * Adblock Plus is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 as
+ * published by the Free Software Foundation.
+ *
+ * Adblock Plus 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 Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/** @module css */
+
+"use strict";
+
+/**
+ * Hides elements on the page using the browser.tabs.insertCSS API.
+ *
+ * @param {string} tabId       The ID of the tab in which to hide elements
+ * @param {string} frameId     The ID of the frame in which to hide elements
+ * @param {string[]} selectors The list of selectors for the elements to hide
+ * @param {Function} callback  The function to be called upon completion
+ * @static
+ */
+exports.hideElements = (tabId, frameId, selectors, callback) =>
+{
+  let code = selectors.length > 0 ?
+             selectors.join(", ") + "{display: none !important;}" :
+             "";
+
+  try
+  {
+    browser.tabs.insertCSS(tabId,
+      {
+        code,
+        cssOrigin: "user",
+        frameId,
+        matchAboutBlank: true
+      }
+    )
+    .then(callback)
+    .catch(callback);
+  }
+  catch (error)
+  {
+    callback(error);
+  }
+};