zastawiałam się dzisiaj dlatego TinyMCE nie działa na jednej stronie, natrafiłam na wytłumaczenie
The error message itself tells you all you need to know to resolve this issue: TinyMCE can only run when the browser is in "Standards Mode" as opposed to "Quirks Mode". TinyMCE did not put your browser in Quirks mode, so if you can solve the issue that caused this, TinyMCE should run.
The most common reason a browser may be put in Quirks mode is if there is no valid DOCTYPE declaration in your HTML document. But there are many reasons a browser can be in Quirks mode. Resolve that, and Tiny should work.
https://tiny.my.site.com/comm/communityQuestion?id=9064N000000MyAoQAK
https://developer.mozilla.org/en-US/docs/Web/HTML/Quirks_Mode_and_Standards_Mode
ogólnie chodzi o to że jak na początku pliku jest cokolwiek przed<!DOCTYPE to TinyMCE nie będzie widoczny
może się komuś przyda