Issue 6437 - Apply :-abp-contains() to matching roots only

lib/content/elemHideEmulation.js

Index: lib/content/elemHideEmulation.js
===================================================================
--- a/lib/content/elemHideEmulation.js
+++ b/lib/content/elemHideEmulation.js
@@ -322,20 +322,33 @@
   },
 
   *getElements(prefix, subtree, styles)
   {
     let actualPrefix = (!prefix || incompletePrefixRegexp.test(prefix)) ?
         prefix + "*" : prefix;
 
     let elements = scopedQuerySelectorAll(subtree, actualPrefix);
+
     if (elements)
     {
+      let lastRoot = null;
       for (let element of elements)
       {
+        // For a filter like div:-abp-contains(Hello) and a subtree like
+        // <div id="a"><div id="b"><div id="c">Hello</div></div></div>
+        // we're only interested in div#a
+        if (lastRoot && lastRoot.contains(element))
+        {
+          yield null;
+          continue;
+        }
+
+        lastRoot = element;
+
         if (this._regexp && this._regexp.test(element.textContent))
           yield element;
         else
           yield null;
       }
     }
   }
 };