Your browser should know how to handle Byteball links after you've installed the wallet on your system.
This wiki entry about installation could be helpful:
https://byteroll.com/installationWell yes, I don't doubt that, but like I said, I keep wallets on an airgapped computer.
I'm looking for eg a simple form where I can copy&paste the signed confirmation message.
Because it's not really complex: post address, get address, sign message, post it.