"Synchronous XMLHttpRequest on the main thread is deprecated" warning
Problem
Someday you might see a warning message in the Javascript console of your browser like this:
Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user's experience.
For more help, check http://xhr.spec.whatwg.org/. Don't worry about it, it will not break TGE or any JIRA functionality.
It is minor warning generated by a browser because of usage of old features of the Javascript
Reason
Actually, synchronous AJAX calls cause this warning. They became deprecated due to possibility to block user interface in case of hanging of the server during the request processing.
JIRA can predict such types of errors and handle them respectively. That is why you can ignore this warning.