Issue 6809 - Implement hide-if-contains snippet

lib/content/snippets.js

Index: lib/content/snippets.js
===================================================================
--- a/lib/content/snippets.js
+++ b/lib/content/snippets.js
@@ -222,8 +222,31 @@
 
       return root;
     }
   });
 }
 
 exports["hide-if-shadow-contains"] = makeInjector(hideIfShadowContains,
                                                   hideElement);
+
+/**
+ * Hides any HTML element if the text content of the element contains a given
+ * string.
+ *
+ * @param {string} search The string to look for in every HTML element.
+ * @param {string} selector The CSS selector that an HTML element must match
+ *   for it to be hidden.
+ */
+function hideIfContains(search, selector = "*")
+{
+  new MutationObserver(() =>
+  {
+    for (let element of document.querySelectorAll(selector))
+    {
+      if (element.textContent.includes(search))
+        hideElement(element);
+    }
+  })
+  .observe(document, {childList: true, characterData: true, subtree: true});
+}
+
+exports["hide-if-contains"] = hideIfContains;