I would imagine it's the MyWay Searchbar which is classified by most anti-malware scanners as adware, or even worse as spyware. I say that because I see "SmileyCentral" in your list of plugins and that's an add-on for that particular toolbar. You can disable that via Tools | Add-ons | Plugins. There are a number of toolbars which won't work with Firefox 4 anymore due to the enhanced protection mechanisms in the browser. Mozilla recommends that you only install add-ons from its own security site @ https://addons.mozilla.org/en-US/firefox/?browse=featured Generally speaking, those have all been tested and approved. The exceptions are those currently under review which are marked with a yellow banner to warn users that they haven't passed Mozilla's labs yet.