This issue is about current implementation of amp-analytics. It is not any browser related. AMP provides 3 different ways to send data with amp-analytics:

• JS Beacon
• XHRPOST
• Image

It works fine with image as all the data gets appended as query param. But with xhrpost and beacon, there is no way to send data as post body. Whats the point of having xhrpost if data can't be sent as post body?