To all —
I was having exactly the same symptoms, except they would only occur on my wireless broadband modem, as opposed to the WIFI I have access to. Became even more confusing than that until I discovered it was isolated to Firefox (I’m on a Mac). Safari did not have the same issue. I did a clean install of Firefox (including wiping the preference files) and that was that.
Maybe this will be of help to some of you.
Dammit Jim, I’m a writer, not a programmer.