Firefox, IE and security issues

I haven't written here in about forever and a half; a couple of projects for a client who wants them yesterday have certainly taken their toll, but hopefully I'll have a bit more time in the near future.

I've been using Firefox as my internet browser of choice for a while now. It really didn't take much to convince me, I was fed up with IE and the security holes - and tabbed browsing surely is very helpful since I tend to have, uhm, "several" windows open at the same time! But promised security was perhaps the most attractive one.

Is Firefox really 100% bullet proof though? I have no interest whatsoever to break into it, but I'm sure sooner or later someone will do that. I am a little suspicious and I have a hard time believing that:

1. Firefox programmers are better than those employed at Microsoft
2. Microsoft did intentionally leave open security vulnerabilities

I am not trying to defend MS by any means. Because of their strategy, their products are still more dangerous. But the reasons why they're more dangerous for the average user, as I see it, are:

1. Internet Explorer, unlike other browsers, is tightly integrated with Windows Operating System. Which means that if one finds a hole in that browser, one can easily take control of the whole machine. One such pitfall would be the infamous MS proprietary ActiveX controls, which can be used to plant unauthorized scripts and open back doors in an unexpecting user's machine.
2. IE is still the most widely used browser in the world. Hence, if one is planning to spend some time and efforts writing code which will get them into as many machines as possible so they can get a good return on their "investment."
   
3. There are far more attacks against MS products (IE, Windows, etc.) than against other ones (e.g. FireFox, Apache, etc.) simply because a lot "programmers" are furious against Microsoft's monopolitistic policies and actions.

In conclusion, I don't think there's any browser which is really bullet-proof. Sooner or later, as Firefox gets more popular, attackers will find exploits in it as well. The best defense strategy is to always be cautious, apply levels of defense (firewall, etc.) and keep browsers up to date with patches released by vendors.