fixup! Bug 27476: Implement about:torconnect captive portal within Tor Browser

Squashed fixup of all the previous #27476 (closed) fixups; fixes:

• #40443 (closed)
• #40441 (closed)
• #40444 (closed)
• #40445 (closed)
• #40446 (closed)
• #40469 (closed)
• #40448 (closed)
• #40455 (closed)