My method of purging evercookie (including emptying cache) works every time I use a wifi connection.
However when I use data tethering using the personal hotspot of my iPhone it usually can still find the etag cookie.
Try it. http://samy.pl/evercookie/
Even completely disabling browser cache in firefox settings does not stop the etag cookies being captured.
Are etag cookies traceable cross device, and if so how do I stop this?