Malicious search plugins can inject code into arbitrary sites — Mozilla

Security researcher Prateek Saxena reported that a malicious MozSearch plugin could be created using a javascript: URI in the SearchForm value. This URI is used as the default landing page when an empty search is performed. If an attacker could get a user to install the malicious plugin and perform an empty search, the SearchForm javascript: URI would be executed within the context of the currently open page.