Disable network prefetch

1596935

• network.dns.disablePrefetchFromHTTPS is now false in FF127+

there are also new prefs

• dom.prefetch_dns_for_anchor_http_document default true
• dom.prefetch_dns_for_anchor_https_document default false
• see https://bugzilla.mozilla.org/show_bug.cgi?id=1596935#c28

see network.dns.disablePrefetch which is default false but we flip to true

edit: some more info: https://github.com/arkenfox/user.js/issues/1870

cc: @pierov simple pref addition