Do you understand that the Unbranded Stable version and Firefox Stable version have the same codebase? You can use that version for testing or if your users don't want signing they can move to that version. They lose the cute icon and branding but the code is the same.
I think you missed my very clear point: now it's not enough to just run Firefox. You need to ask for users to run the "right" version if Firefox.
Telling people what browser to use is user hostile behaviour. Users will not bother. Non-official extensions will get less interest. Authors will see a smaller user base and have less interest in writing new extensions.
