If you get an error message when opening the editor ('Failed to initialize plugin:...'), please clear your browser cache, close your browser and then reload the page.
 
Procedure for deleting your browser cache:
 
Chrome
Settings->Privacy and security->Clear browsing data->Cached images and files
 
Firefox
Settings->Privacy and security->Cookies and website data->Remove data
 
Edge
Settings->Privacy, Search and Services->Clear browsing data
 
Safari
Safari->Clear History and Website Data