Hi,
I can produce an error by following that url too but it does not break the editor. The reason it has an error is because additional paramters are expected and would be passed in by the editor to do spellchecking. Thats is just the base url configured on the editor, but the editor passes in more query string params when it uses that url.
Nothing about that code has changed in this version or in any version in a long time.
The error:
tinymce is not defined.
is a javscript error that sounds more like the TinyMCE script is not loaded correctly.
I recommend use the Web.config file that shipped with mojoPortal, don't just try to update yours, you might have missed other things.
Your url also looks problematic:
http://localhost/mojoPortal.Web/
I do not recommend using a . in the folder name that can cause problems, please try changing the folder name where you are running mojoPortal to not have a dot.
Hope that helps,
Joe