This happens when the extensions are not signed. Firefox doesn't allow installing extensions that aren't singed anymore. You will have to download latest version of Firefox and Kaspersky to update the current installations, then try installing the extensions as well. If it still doesn't work after this procedure, then you need to forward a complaint to Kaspersky support. They need to send the extension to Mozilla for signing and then you can install it.
Kaspersky Support: http://support.kaspersky.com/
