Browsers need to be more eager to offer workarounds for things like... that dang snake oil TLS cert on the ISP's router setup in a weird way but in the 'reserved' private use address ranges.

NOT automatically, but with an accommodation that asks the user if they're _expecting_ to talk to a device such as a "Modem" or "ISP Router" when making that request, and offer to do what's necessary to connect.