Yes. All extensions have to be signed by Mozilla, even if they're distributed outside their directory. The only way would be able to install it is by downloadin

Yes. All extensions have to be signed by Mozilla, even if they're distributed outside their directory. The only way would be able to install it is by downloading an unzipped version and sideloading it. However, it will be removed if you restart firefox, and you will have to re-add it.