Does anyone know of a way to "build in" foxyproxy to an install of Firefox?
I want to roll this out to many users and have several extensions pre-installed.
Foxyproxy and "mismatched domain".
I found the post on how to let foxyproxy point to a common filter rule.

There's probably more than one way to do it, and this isn't the best place to ask (try forums.mozillazine.org) since this is a general packaging/deployment Firefox question, but one way would be to use Portable Firefox.

Portable Firefox doesn't have to be used on a USB thumbdrive. You can install it on a harddrive simply by copying/pasting one directory. So, to "preinstall" extensions, you could install them into your copy of PFF then simply copy your PFF directory to the other machines.

Note that if you use FoxyProxy with PFF, you need to check the appropriate checkbox in the Global Settings tab.