Recently, I have noticed this error in my Chr***m-related browser's console:

[Deprecation] Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user's experience. For more help, check h****://..**./.

How can I anticipate that a browser will do this and create a workaround for what sounds like intended to become an API which can no longer be used?

I'm intending to maintain compatibility with older browsers indefinitely, so removing this behavior is not something I can remove outright, but I can perhaps feature-check around it?