You may have heard of the the Firefox Build Your Own Browser Project. On the web page, it says it "is a simple way that your organization can create and distribute a customized version of Firefox." I think BYOB is a great start to solving the distribution problem, but it's missing one key thing - the ability to bundle your own add-ons.
What I'm going to do with this post is explain exactly how BYOB works internally so that you can create your own distribution that has all the customizations you want. There are a some downsides to our method - primarily that we are Windows only and that we can't sign our installers with the Mozilla certificate. But it's the only way we can create a distribution that includes our own add-ons.