That's weird LOL Yeah I have a few like Firebug and Text Translator, I'll disable them and see if that works.I can't reproduce this in FF 44.0.2 either...
Do you have any browser extensions installed? Might be worth disabling them all and trying again.
IPv6 Learning Center
Data Sources and APIs
Public IP Address
Scripted access to our homepage or IP details pages are not permitted.
We provide several pages that return just the public IP address of the device making the request. You may programmatically query that server but limit queries to no more than once per five minutes and include an appropriate user agent that will allow us to contact you if needed. Requests with a blank user agent may be dropped.