It starts with the words "As part of our continued collaboration with Anthropic"
Once these words are used you can assume there is a contract stating how that collaboration works, and that this includes some sentences about how much each side is allowed to or required to say about it
So you claim that Mozilla entered into a contract with Anthropic, and said contract requires Mozilla to advertise for Anthropic on their blog. I hope Mozilla is getting a good payday out of this.
Once these words are used you can assume there is a contract stating how that collaboration works, and that this includes some sentences about how much each side is allowed to or required to say about it