It’s about their FakeSpot subsidiary.

https://support.mozilla.org/en-US/kb/review-checker-review-quality#w_protect-your-privacy

Protect your privacy Firefox is committed to empowering you with information about review reliability while respecting your privacy. We use Oblivious HTTP (OHTTP) for Review Checker. When Review Checker is turned on, we use information about the products you visit on Amazon, Best Buy and Walmart to analyze the reviews, but by using OHTTP we ensure Mozilla cannot link you or your device to the products you have viewed. OHTTP uses encryption and a third party intermediary server to offer a technical guarantee that this is the case: all Mozilla learns from this network request is that someone, somewhere, looked at a given product.