Comment 45 for bug 314713

This bug also affected me. But changing MTU to 1360 fixed it.

I was surprised when it worked. I am guessing that HTTP is forwarded over some link with a smaller MTU and "Don't Fragment" set. You can ping the site with packets upto 1500 bytes. But sending HTTP with packets of more than 1400 bytes, gets no response at all, presumably they don't get through to their server.

Believe it - it really works.