"“Beware of spyware. If you can, use the Firefox browser.” - USA Today"
"Privacy and Security
Built with your security in mind, Firefox keeps your computer safe from malicious spyware by not loading harmful ActiveX controls. A comprehensive set of privacy tools keep your online activity your business."
While that's technically correct - Firefox couldn't (can't?) load ActiveX controls, therefore it could't load harmful ActiveX controls - the Firefox extensions system has permitted installation of executable code for a long time, if not since its inception. Since that's what ActiveX is, more or less, Firefox has never been any more secure in that respect than e.g. Internet Explorer.
Like Apple products, as Firefox becomes more popular (and therefore a jucier attack target) there will be more malware that targets it.
Edit: Fix typo.
I'm presenting some pertinent history and tying it to the recent Apple malware news, which has been heavily discussed here.