on my main 'working' pc, i just have two firefox. one regular release channel, locked down pretty tight--scripts don't even run unless allowed, used for the bulk of the internets; and then a developer edition with a different config and different selection of addons that i use for the trusted and internal sites and 'my' stuff.

dev.ed is made to co-exist with 'regular' firefox; can even run both at the same time without any hoop jumping as dev.ed profiles are separate.