Youtube still works as normal (no ads, no problems) for me with the latest Firefox and uBlock Origin.
Could this be a country-specific thing?
Firefox said it will adopt Manifest V3 in the interest of cross-browser compatibility.
https://www.malwarebytes.com/blog/news/2023/11/chrome-pushes...
Manifest V2 is the old model. The Chrome Web Store no longer accepts Manifest V2 extensions, but browsers can still use them. For now. Manifest V3 is supported generally in Chrome 88 or later and will be the standard after the transition planned to take place in June 2024.
https://developer.chrome.com/docs/extensions/reference/decla...