Ok, I’ve updated the plugin to properly support the new emoji picker in Discourse 
https://github.com/gdpelican/retort/commit/4f5f3168ba15a905996badb180b3688f63067eeb
It’s been tested in full and limited mode, and also on mobile. You can test it out here yourself:
That site gets automatically rebuilt every 24 hours (which updates it to the latest Discourse). So if you’re on tests-passed (the default branch) it’s a good idea to test out any custom plugins you’re using there before you update.
I’ve also added a .discourse_compatibility file to the plugin:
https://github.com/gdpelican/retort/commit/35aaad57860148d2491021084379614d31f5eb6e.
This means that if you’re running the stable branch of Discourse you can keep updating as normal and this plugin will stay pinned at a commit that works with the latest stable release. See further here:
Pinning plugin and theme versions for older Discourse installs.
In this case the last stable release of Discourse (2.5.1) was 2 weeks ago and the emoji-picker refactor that broke Retort was 10 days ago, so the stable commit for this plugin is https://github.com/gdpelican/retort/commit/92738f00fce990fa6a6027016bb82845a4c6c8a1 which I made back in June (tested and working with stable 2.5.1).