I was having that problem as well. When the screen goes blank, back up one screen and refresh the thread. In all cases, when I did that, my post has appeared.
For some reason, that glitch stopped on its own when Firefox 26.0 upgraded itself to 26.0.1.
Just go to Firefox (orange box in upper left corner), Help, and then About. Firefox will upgrade to 26.0.1 if you’re still at 26.0.
Hope this helps.
NC shall soon see. I rebooted this old LT and numerous updates were ready to install.
A reboot did the trick.
Make sure this is disseminated through-out FR land.
Happy Wednesday! :^)