Issue 5015 - Better handle broken element hide filters

include.preload.js

Index: include.preload.js
diff --git a/include.preload.js b/include.preload.js
index 1d4635a0da9fcda4266406564256e040e164b877..df6f9a105b52f0918f2c053a7b72dbb8f76df01b 100644
--- a/include.preload.js
+++ b/include.preload.js
@@ -482,6 +482,36 @@ ElemHide.prototype = {
     return shadow;
   },
 
+  _insertRuleForSelectors(selectors)
+  {
+    const properties = " {display: none !important;}";
+
+    try
+    {
+      this.style.sheet.insertRule(
+        selectors.join(", ") + properties,
+        this.style.sheet.cssRules.length
+      );
+    }
+    catch (batchInsertException)
+    {
+      // There is a syntax error in one or more of the selectors. Rather than
+      // dropping all of them let's add them invdividually, so that only the
+      // broken selectors are skipped.
+      for (let selector of selectors)
+      {
+        try
+        {
+          this.style.sheet.insertRule(
+            selector + properties,
+            this.style.sheet.cssRules.length
+          );
+        }
+        catch (individualInsertException) {}
+      }
+    }
+  },
+
   addSelectors(selectors, filters)
   {
     if (selectors.length == 0)
@@ -528,11 +558,9 @@ ElemHide.prototype = {
     // [1] - https://github.com/WebKit/webkit/blob/1cb2227f6b2a1035f7bdc46e5ab69debb75fc1de/Source/WebCore/css/RuleSet.h#L68
     for (let i = 0; i < preparedSelectors.length; i += this.selectorGroupSize)
     {
-      let selector = preparedSelectors.slice(
-        i, i + this.selectorGroupSize
-      ).join(", ");
-      this.style.sheet.insertRule(selector + "{display: none !important;}",
-                                  this.style.sheet.cssRules.length);
+      this._insertRuleForSelectors(
+        preparedSelectors.slice(i, i + this.selectorGroupSize)
+      );
     }
 
     if (this.tracer)