Firefox found a way to keep ad-blockers working with Manifest V3
A manifest tells the browser all sorts of information about an extension, from what its name and version number are, to what permissions it'll use, and what versions of a browser it'll run on. New versions of the Manifest file format used by the browsers change what features extensions have access to, and can mandate changes.
https://www.theverge.com/2023/1/17/23559234/firefox-manifest-v3-content-ad-blocker