Custom FireFox Browser

I am interested in building a very basic custom browser. I did a quick Google search and found BYOB (Build Your Own Browser) by Mozilla, but that project was shut down some time ago.

My reason for needing a custom browser is simple, but I am open to other solutions. I have developed a UI for configuring a hardware device, similar to how you customize your router via a web based GUI. My GUI is compatible with IE, and FireFox, but a common issue is the release of new browser versions and not being backwards compatible. I would like to allow my customers to be able to download our custom browser that directs them to their hardware device and basically only allows the user to go to one site, which is the IP address of their hardware device so that they can configure it using my software. The custom browser will essentially be locked at a specific version that will always be compatible with my software and thus preventing a lot of headaches in my future, and also allows my company to never need to support my software if I get hit by a bus. They can just rely on our custom browser being able to work for years to come, as nothing should change. Also, any future developers on this platform will only have to be compatible with ONE browser, our custom browser.

Google has not provided enough to go on. Has anyone else done this or something like this?