Secure?! I don't think so. Now there is more security flaws discovered in firefox than in IE! Personally I have nothing against any software but don't say secure if you first don't check Secunia for example (3 vulnerabilities not fixed in FF now).
I don't use FF cause installation of those extensions drives me crazy. Especially when it comes out that they're not compatible with FF although they should be
I use Opera - cause it's fast, stable and secure. But - who cares?!