Browsers are terrible at accessing devices on a local network. Make this work well in Firefox, extending protocols as needed.
Browsers are terrible at configuring IoT devices. It device makers are terrible at making apps for this purpose that don’t suck. Make Firefox (on desktop and mobile!) be the premier way to usable and securely configure IoT devices. Get device vendors to sign on: someone could (and probably would) sell a gadget where the instructions suggest installing Firefox to set up the device.
Leverage the same technology to go after enterprise users. Ever seen a piece of high-end, expensive networking gear with a web UI? Ever contemplated how pathetically insecure this is? Ever contemplated how unpleasant it to provision certificates to make it secure? Make this work, easily and securely, on Firefox, using new protocols as needed. Make everyone else play catch-up.
Heck, start small. Allow setting domain constraints on imported root certificates.
The moral: do something new and better.