Did Mozilla signal any intention to phase out V2 though? It makes sense for them to support both, as a lot of extensions (that don’t rely on V2 features that are missing from V3) are going to be built for V3 now and if Mozilla wants to keep their extension store full. If they didn’t offer both versions, extensions developers might disregard Firefox as a platform because of its low usage share numbers if they had to maintain two different architectures.