You can make the FF work by typing into the adress bar this: about:config
and then do this:
Set “network.http.pipelining” to “false” - by double clicking on it.
Set “network.http.proxy.pipelining” to “false” - by double clicking on it.
Set “network.http.pipelining.maxrequests” to what it was before - it's currently at 30, right? If you can change this back to its default, then do that. Right click on it and choose reset, and it should go back to what it was.
Then you need to change “nglayout.initialpaint.delay” back to what it was, again by right clicking and resetting.
That will solve the problem.