User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:44.0) Gecko/20100101 Firefox/44.0 Build ID: 20151012030612
I am guessing you have e10s enabled correct?
I have looked across all about::'s, but I cannot find e10, anywhere.
Are the unlisted plugins exposed to websites? Test page: https://www.jeffersonscher.com/res/plugins.html With the x64 build you would only expect Flash and Silverlight to be activated.