I just read about the JSON update file, introduced with FF 45:
https://blog.mozilla.org/addons/2016/02/05/compatibility-for-firefox-45/
How do I have to do the “signature” like in the update.rdf?
Example:
Quoting from the bug report:
The “update_link_key” property shouldn’t be implemented in the first
version, but I think it would be a good idea plan on allowing pinned keys
for both the update link in manifest.json and the update links in
update.json in the future, for people who insist on added security.
So, if you need to use the signature feature, you’ll need to continue using the old format, at least for now.