Some enterprising spyware distributors have managed to make browsing with Firefox, Mozilla, and Netscape dangerous. They've engineered a Java applet that initiates spyware downloads when you browse a site with the aforementioned browsers. Vitalsecurity.org has the article describing the exploit in detail. The spyware that gets downloaded is your standard garbage. It will use Internet Explorer (IE) to deliver its pop-ups, which can be particularly annoying if you had shelved IE long ago in favor of Mozilla-type browsers. Also, you need to have the Sun Java runtime installed and active for the exploit to work, and you also need to click OK in a dialog box to begin downloading the spyware. Most people that have made the switch to Firefox are smart enough not to click Web-generated dialog boxes.