These are great points but also speak to one of my concerns about forking--what if Firefox continues to receive lots of security scrutiny but this new-but-still-pretty-intimately-related product aimed at devs mostly doesn't, for whatever reason (e.g. far fewer people using it)?
I see more value for both developers and users currently because it means that in order to keep Firefox safe (for some definition of safe), the Mozilla security team also has to keep people like us--and the functionality we use--just as safe. It also means derivatives like the Tor Browser Bundle and Iceweasel might be more likely to preserve the feature set and benefit from security team's work in relation to it.
I see more value for both developers and users currently because it means that in order to keep Firefox safe (for some definition of safe), the Mozilla security team also has to keep people like us--and the functionality we use--just as safe. It also means derivatives like the Tor Browser Bundle and Iceweasel might be more likely to preserve the feature set and benefit from security team's work in relation to it.