Also re-enable the JIT, as the jit may cause faster element loading to happen
(which will result in better pipelining request availability).

We can't easily bind SSL Session ID tracking to url bar domain,
so we have to disable them to satisfy
https://www.torproject.org/projects/torbrowser/design/#identifier-linkability.

This disables the disk activity entirely. It seems as though there is no
reason in to write backup copies of clipboard data to disk, as the clipboard
code does not release the related memory upon disk writes anyway.

See https://trac.torproject.org/projects/tor/ticket/9701.

It's possible to construct a request where the Host header differs from
the authority in the URL, for example in an extension with
nsIHttpChannel and setRequestHeader. MakeConnectString generates a
host:port string for the CONNECT Request-Line, but peeks into the
tunneled request in order to copy the Host header to the proxy request.

Instead, use the same host:port string for Host as is used in the
Request-URI, to avoid revealing the plaintext of the Host header outside
of the tunnel.

Backport of https://hg.mozilla.org/mozilla-central/rev/a1f6458800d4.

Includes:
https://hg.mozilla.org/mozilla-central/rev/7b86302ab2b3
https://hg.mozilla.org/mozilla-central/rev/1651ea86cb00
https://hg.mozilla.org/mozilla-central/rev/fda0046aa376
https://hg.mozilla.org/mozilla-central/rev/02d4ae55e1c3