Fixing bug 265921. Prevent script from closing tabs. r=bryner@brianryner.com, sr=brendan@mozilla.org, patch by bzbarsky@mit.edu and jst@mozilla.org

browser/base/content/tabbrowser.xml

@@ -1408,6 +1408,9 @@
 
       <handler event="DOMWindowClose">
         <![CDATA[
+          if (!event.isTrusted)
+            return;
+
           const browsers = this.browsers;
           if (browsers.length == 1)
             return;