https://blog.mozilla.org/addons/2022/11/17/manifest-v3-signi...

> Towards the end of 2023 [...] we’ll decide on an appropriate timeframe to deprecate MV2.

https://blog.mozilla.org/addons/2024/03/13/manifest-v3-manif...

> Firefox, however, has no plans to deprecate MV2 and will continue to support MV2 extensions for the foreseeable future.

Seems they changed their mind in 2024.