I am using Mozilla(Firefox) as my first choice Internet Browser since a long time.
A main factor for not using the Internet Explorer was (and is) the security risk (not only) caused by the wide spread of the IE.
But as Mozilla (Firefox) becomes more and more popular, Mozilla is getting more interesting to coders of malicious software as well.
A very good (german) article can be found here.
First I was a bit shocked, because I thought to be on the safe side because of using Mozilla instead of Internet Explorer, but then I realized that even a possible more secure browser will not protect you complete, if you trust almost everything in the web.
The key point here is that the most important security guideline is a common mistrust of any web content.
“Wer auf alles klickt, was ihm irgendwo unterkommt, wird sich früher oder später einen Schädling einhandeln — egal welchen Browser oder welches Betriebssystem er nutzt.”