jQuery 2.x not allowed in Firefox Addons
According to https://github.com/mozilla/addons-linter/blob/master/docs/third-party-libraries.md :
2.x: jQuery 2.x is no longer supported by the jQuery team. Due to open security vulnerabilities, you should migrate to jQuery 3.x as soon as possible. Starting September 2018, add-on submissions using jQuery 2.x will no longer be allowed.
jQuery 2.x is still there because some code in the background script has been kept from v1 and because jQuery is used in mirrors implementations.
We need to move to 3.x and fully test background script and mirrors