I was accessing an internal router with firmware from the distance past of 2011. Note that this is an internal-only router that connects a couple of trusted subnets, so security isn't an issue and there's no requirement to replace it yet. The problem that bit me yesterday was that I literally could not find a way to get Chrome to open https://ro.ut.er.ip/ because the router's ancient cert is invalid.
I would have been perfectly fine with Chrome alerting me to that fact and providing a "click here to continue anyway" link, but that seems to no longer be an option. FWIW, Safari did the exact same thing. Only Firefox gave me the "I promise that's really what I want to do step aside plz" button I needed.