config.filebrowserBrowseUrl = './workspacebrowser.jsf'; config.filebrowserWindowWidth = '600'; config.filebrowserWindowHeight = '600';
window.opener.CKEDITOR.tools.callFunction(funcNum, fileUrl);
CKEditorFuncNum=undefined
http://localhost:8080/nymphaea/pages/workspacebrowser.jsf?CKEditor=j_id313:contentAreaDataTable:0:formcontent:content&CKEditorFuncNum=undefined&langCode=en

Re: Custom File Browser: CKEditorFuncNum=undefined
I simply changed ckeditor.js with ckeditor_source.js and now I get the CKEditorFuncNum correctly.
I have no idea, what has changed.