Current spec at https://developer.mozilla.org/en-US/docs/Apps/Manifest#description says the description can be 1024 characters. We current limit to 250.
https://github.com/mozilla/zamboni/commit/2d70937 is the 1st part. Next part is the app-validator fix and bump.
This isn't fixed on prod (though the target date would indicate it should have been): https://marketplace.firefox.com/reviewers/apps/review/twinkle-pang (I did a force refresh after clearing the review)
It should be pushed this Thursday.