Closing the HelpTool can sometimes produce the following Javascript error :
Error: Permission denied to access property "removeEventListener"
element.dom.removeEventListener(eventName, capture ? this.onDirectCaptureEvent :...
ext-all-debug.js (ligne 32316, col. 9)

If this error occures, the javascript is broken, and the application becomes unusable (buttons stop working, can't close tool, ...).

I have the default workspace configuration (sitemap + welcome page) and the notification tool opened.
I did not reproduce on chrome.