Follow-up: Two weeks ago I asked about how Firefox' new AI chatbot integration fares regarding privacy.
By accident I found information on it in Mozilla's knowledge base [1] and a related article by them on privacy and chatbots [2].
Short answer: Mozilla does not read conversations, but some metadata is collected. Chatting with chatbots has the usual implications.
Some answers in the FAQ [1] I found particularly helpful, see screenshot.
[1] https://support.mozilla.org/en-US/kb/ai-chatbot
[2] https://foundation.mozilla.org/en/privacynotincluded/articles/how-to-protect-your-privacy-from-chatgpt-and-other-ai-chatbots/