content: Firefox is the only major browser that isn't sandboxed yet - so having access to it means you get access to the OS pretty easily and straightaway you can see it's not up to the standards of its competitors.  It also got destroyed at last year's pwn2own with gaping holes of security and it didn't fix much of the problems it had - their biggest security improvement was pushing for signed extensions last year, which means little to pwn2own since browsers there are exploited in default installations - and as such having Firefox there would simply be a waste of sponsor money since Mozilla is unwilling to do anything with the data reported as shown from the past few years. In all, no need to go conspiracy on something that is easily explained.