I didn’t think so really, if you look at the release notes for pale moon you can see they do plug vulnerabilities monthly but someone may know better about this stuff than me. I should probably add a note here about the open source community often being far more on it than the large platforms, particularly microsoft (screams silently) either refusing to acknowledge problems for a long time or updates that fuck something else up.
Ghacks have a review of what mozilla should now do to prevent this happening in the future and allowing already installed extensions to still run if the user wishes should be implemented and i agree, it’s completely daft an expired cert on mozilla’s end should block your installed extensions.