This is a bit awkward, and I hope you will forgive me for not explaining exactly how it happened, but I ended up deleting logged-in.js , and now tinymce won't work on my Plone site.
I know I can recover a backup ( which I have ) and solve the problem in this way, but part out of laziness and part out of curiosity, is there a way I can recover just this one script? I can get the script pretty easy from another Plone site, but what I don't know is how and were to drop it in the site where it is missing.
It's located in YOURSITE/portal_resources/resource_overrides/production/manage. From there you can try to use the Undo tab, if it doesn't work you can try again in the ZMI root, but you'll have to undo also all transactions that happened after the deletion (at least to recover the file, then you can redo them all).
Okay, problem solved. I exported the script from portal_resources/resource_overrides/production/manage of another site and imported it where it was missing.