Recently I found a nasty problem with Typo3’s richt text editor (RTE) when a non-admin user was logged in. (Typo3 version 4.5.25)
Trying to open a content element with a rich text editor field, presented only the message “editor is being loaded” without any further information or progress.
When logging into the backend as an admin user, everything worked fine.
Checking with the firefox javacript console, the following error was provided:
ReferenceError: invalid assignment left-hand side
Line: 414, Row: 60
3);return('#'+hex(r)+hexHTMLArea.Editor.prototype.isEditable=function(){return(this._doc.designMode==="on");};HTMLArea.E
Finally, the solution I found was to disable the javascript compression for the richt text editor scripts in the extensions overall configuration using the Extension Manager:
However, this was the first time I saw this problem and I was not able to reproduce it on any other of our typo3 installations.