Also a very important point in the article is that Internet explorer still in top of attacks

That said, Internet Explorer remains the most popular target for attacks, with 69 percent of all browser attacks targeted specifically at that browser alone. 20 percent of the attacks monitored during the period in question were targeted at Firefox.

When it comes to patching, all of the browsers are improving. Firefox is the fastest to get its patches out, with a one-day window of exposure. Opera had a two-day window of exposure, down from 18 days during the last half of 2005. The window of exposure for Safari is up to five days (from zero), while Internet Explorer typically has a nine-day window, down from 25 days in the previous study.

But if we go back to the study and the way it have been done, you should know that such studies are based on discovered bugs. And while Firefox is open source, Internet explorer is proprietary sources and have lot of bugs which remain unkown for the public, used for attacks and never been patched.

If you check Firefox vulnerabilities that the report was talking about you'll find them all fixed and patched in the latest release. Now check the IE bugs and try to find out a patch or a fix !! I remember the last patch IE released, few days later they released another patch to patch it !!

With Firefox I feel more secure for many reasons, first the code is open and bugs are easy to find and fix, secondly as soon as a vulnerability is discovered its quicker patched, and finally the Community of Firefox users is very large which make discovering bugs and make them fixed more easy. While Opera and Safari the community of users still very small compared to IE and Firefox, that's why reporting the number of vulnerabilities only is not relevant information at all. Firefox even vulnerable, it's more secure browser !