On sites that leverage the Granite i18n javascript library (for example: Granite.I18n.get("");), the error below is observed in the javascript console of the browser:
[Deprecation] Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user’s experience. For more help, check https://xhr.spec.whatwg.org/.
The synchronous ajax call is by design. Adobe Engineering team plans to change this functionality in the future by loading the file via including a script tag. However, that product enhancement won't be included in AEM until a future version.