The problem appears to be similar to this one: https://support.mozilla.org/en-US/questions/986709?fpa=1 , however it is only happening randomly. It only seems to be a 30-40% chance of happening when I visit a domain that I don't visit very often or have never visited and ~5% of happening once per (sub)domain per browser session. I am very sure that it is not a connection problem as I have not had any problem with any other browser or internet using program and the problems did not appear before updating to FF 27(.0.1).