It's malware, so you are right not to want to install it. Can you run other Firefox windows? You could try a bookmarklet to zap the page. Three steps: (1) Open my bookmarklets page here: http://dev.jeffersonscher.com/bookmarklets.html (2) Right-click the Escape button and choose Bookmark This Link, or if you see a convenient spot on your Bookmarks Toolbar, you can click and drag the button there (3) Back on the problem page, cancel the dialog (stay on page) and then click the Escape button -- wherever you added it (e.g., Bookmarks Toolbar or Bookmarks Menu) -- it should zap the page so you can then close it Does that work?