Hi

In three browser families researched (Edge, Internet Explorer and
Firefox - all on Windows 7 or above), it is possible to extract the
frequency of the Windows performance counter, using standard HTML and
Javascript. With the Windows performance counter frequency, it is
possible to remotely detect some virtual machines and to coarse-grain
fingerprint physical machines.

The full advisory is here:

http://www.securitygalore.com/site3/vmd1-advisory

A demo page for this advisory is here:

http://www.securitygalore.com/files/vmd1.html

A fix is available in Firefox 41:

https://www.mozilla.org/en-US/security/advisories/mfsa2015-114/

Finally, you may be interested in my page dedicated to web-based VM
detection methods:

http://www.securitygalore.com/site3/web_based_vm_detection

Thanks,
-Amit
http://www.securitygalore.com/