The Standalone WYSIWYG editor doesn't load in Firefox after enabling the "Load JavaScript Skin Extensions" configuration

This affects only the standalone WYSIWYG edit mode when using Firefox, after enabling the "Load JavaScript Skin Extensions" CKEditor configuration from the wiki administration.

It's very easy to reproduce: just edit the Sandbox home page in standalone WYSIWYG mode before and after enabling the "Load JavaScript Skin Extensions" configuration. Outcome: the editing area is empty and read-only.