Although I use Firefox in preference to Internet Explorer, I do so for features such as tabbed browsing.
Vague claims that it is "more secure" have never washed with me: how do you prove it? I can prove that one piece of software is faster than another or easier to install or costs less but proving something is more secure (as opposed merely to having had fewer security problems discovered in it) is an entirely different question.
So those who spend their days trumpeting Firefox (or Apple's Operating System for that matter) as somehow superior than a competing product because they are "more secure" attract my disapproval (and you don't want to be the target of my disapproval!)
I therefore felt a sense of schadenfreude when I read this article. It appears that Firefox's Java Script engine is a "complete mess" and quite likely riddled with security holes. Who'd have guessed it?!
(For the record, however, I should say that I do not approve of those who don't give vendors sufficient time to fix problems before publishing.)