You have to change settings in about:config, e.g. `browser.ml.chat.provider = http://localhost:3333` with the address of your model server (I actually use open-webui with ollama for that).

Then you could change the prompts, for example, those are mine :

browser.ml.chat.prompts.0 {"id":"search", "value": "What do you know about the selected text?", "label": "Search"}

browser.ml.chat.prompts.1 {"id":"grammar", "value": "Can you fix the grammar in the selected text?", "label": "Grammar"}

browser.ml.chat.prompts.2 {"id":"summary", "value": "Can you summarize the selected text?", "label": "Summary"}

browser.ml.chat.prompts.3 {"id":"code", "value": "Can you explain the selected code?", "label": "Code"}

browser.ml.chat.prompts.4 {"id":"translate", "value": "Can you translate the selected text?", "label": "Translate"}

I have found instructions here https://connect.mozilla.org/t5/discussions/advanced-configur..., though they are a bit outdated since you have to setup prompts differently.