Filter Preferences: Template conditions not evaluating to a boolean are interpreted as true

chrome/content/ui/filters.js

Index: chrome/content/ui/filters.js
===================================================================
--- a/chrome/content/ui/filters.js
+++ b/chrome/content/ui/filters.js
@@ -131,17 +131,22 @@ var Templater =
     {
       if (node.localName == "if")
         conditionals.push(node);
       for (let i = 0; i < node.attributes.length; i++)
       {
         let attribute = node.attributes[i];
         let len = attribute.value.length;
         if (len >= 2 && attribute.value[0] == "{" && attribute.value[len - 1] == "}")
-          attribute.value = Cu.evalInSandbox(attribute.value.substr(1, len - 2), sandbox);
+        {
+          let value = Cu.evalInSandbox(attribute.value.substr(1, len - 2), sandbox);
+          if (attribute.name == "condition")
+            value = value ? "true" : "false";
+          attribute.value = value;
+        }
       }
     }
 
     // Process <if> tags - remove if condition is false, replace by their children
     // if it is true
     for each (let node in conditionals)
     {
       let fragment = document.createDocumentFragment();