Hi there. You cant create browser extension with java, you can do it only with javascript.
As for the bot itself, maybe there is some service that already exists and I can use the API to use its functionality. As far as the custom-made bot, it will be very simple, because the technology that is used to create an extension (javascript) is not made for that kind of things. It can send messages, with pauses, can name user with a name, and also some very simple logical answers. But that's it.
Also, when do you plan to start this project and when is the deadline, if there is one. Also, what would be the salary for this development?
Anyways, feel free to hit me up so we can talk more about this. I am very responsive. All the best