the VMware Client Integration Plugin has updated its SSL certificate in Firefox
With the recent release of Mozilla Firefox and Google Chrome, the ability to start the VMware Client Integration Plugin again be broken. vSphere Web Client 6.0 constantly displays pop-up message, as follows:
This is because the two browsers are removed support for NPAPI plugins. Therefore, it will remove some of the operations for the Web client, such as the deployment of OVF or OVA template and use the data store browser to transfer files.
I found the problem only viable solution is to use Firefox 52 support extended version (32-bit version), it will support NPAPI plugins until early 2018.
Or, upgrade to version 6.5 vCenter Server Appliance should, where "VMware enhanced authentication plug-in will replace vSphere 6.0 and earlier versions of Client Integration Plug-in", and does not require NPAPI support.
21/06/2017 - Update 1: When the Web browser is configured to use a proxy server, this message will pop up. Switch to the "no proxy" mode so that it can not be displayed.