SecurityError: The operation is insecure - window.history.pushState()

Make sure you are following the Same Origin Policy. This means same domain, same subdomain, same protocol (http vs https) and same port.

How does pushState protect against potential content forgeries?

EDIT: As @robertc aptly pointed out in his comment, some browsers actually implement slightly different security policies when the origin is file:///. Not to mention you can encounter problems when testing locally with file:/// when the page expects it is running from a different origin (and so your pushState assumes production origin scenarios, not localhost scenarios)

You should try not open the file with a folder-explorer method (i.e. file://), but open that file from http:// (i.e. http://yoursite.com/ from http://localhost/)

In my case I was missing 'www.' from the url I was pushing. It must be exact match, if you're working on www.test.com, you must push to www.test.com and not test.com

We experienced the SecurityError: The operation is insecure when a user disabled their cookies prior to visiting our site, any subsequent XHR requests trying to use the session would obviously fail and cause this error.