This can happen with Twitter etc as well.
open a new firefox window
type ”about:config” into your URL.
search for “spdy” and double click on”network.http.spdy.enabled” so that it is “disabled“
What does SPDY do?
SPDY is an experimental networking protocol developed primarily at Google for transporting web content. Currently it is not a standard protocol. SPDY is similar to HTTP, with particular goals to reduce web page load latency and improve web security through compression, multiplexing, and prioritization.