Open firefox's error console (κονσόλα σφαλμάτων), clear the messages and refresh the page. Try to write something and click save. Copy-paste here the error message you get or show us a screeshot of the error console.Firefox toolbar -> Tools -> Error console.
Thanasis the errors you pasted are just css errors, nothing special. I need to see the problem in action to find out which is the problem. Does the editor works for the rest elxis pages? Maybe acampball can help you more in this.Editor is working fine for the rest elxis pages.