Whenever I try to post something using Firefox I get the above message.
I don't get this with other browsers and, I don't have problems with any other sites - just WC.
Make sure you are not using any ad-blockers and that the browser is up to date. Not seeing any issues here.
Are you using privacy badger? Its automatic blocking has a tendency to block the editor scripts.
Yes,it happened to me by using ad block of kinds.
Congratulations! You win the cuddly toy!
You should start using other browsers too! Try Opera, I love it! Why? It literally never crushes, never.
Personally, I only use browsers that crush.