In among the general rejoicing at Mozilla over these figures on browser share there'll be a few worried faces in the developer labs.
You could argue until the cows come home over the security benefits of open versus closed source. I happen to think that open source is more secure and quicker to patch than commercial companies.
But all major code is unsafe; it will have flaws by its very nature. You can't have millions of lines of code and no mistakes, at least not until the gods start coding.
But the more popular Firefox becomes the more hackers will target it. The hacker, no matter if they're motivated by kudos or cash, will usually go for the largest number of users, and that means a popular browser.
So well done to Firefox, but also a warning: the Mozilla boys are going to need to be on their toes for a long time to come.