STR:

• use mayhemer/node_http2_proxy: A simple HTTP/2 proxy with CONNECT method support based on Node.js
• system is ipv6 enabled
• internet is not ipv6 enabled
• no exception for detectportal domain
  => peerAddr == "127.0.0.1"

this check probably can't be done when a proxy is there and when it listens only on ipv4 (despite it's configured to listen on any address - 0.0.0.0)

>	xul.dll!mozilla::net::NetworkConnectivityService::OnStopRequest(0x000002aea3b4a050, NS_OK) Line 281	C++
 	xul.dll!mozilla::net::nsHttpChannel::ContinueOnStopRequest(NS_OK, true, true) Line 8295	C++
 	xul.dll!mozilla::net::nsHttpChannel::ContinueOnStopRequestAfterAuthRetry(NS_OK, false, true, true, 0x0000000000000000) Line 8125	C++
 	xul.dll!mozilla::net::nsHttpChannel::OnStopRequest(0x000002aea1e90d40, NS_OK) Line 8056	C++
 	xul.dll!nsInputStreamPump::OnStateStop() Line 656	C++
 	xul.dll!nsInputStreamPump::OnInputStreamReady(0x000002aea555c310) Line 403	C++
 	xul.dll!nsInputStreamReadyEvent::Run() Line 91	C++
 	xul.dll!nsThread::ProcessNextEvent(false, 0x000000e5339feb3f) Line 1227	C++
 	xul.dll!NS_ProcessNextEvent(0x000002ae9d85c1c0, false) Line 486	C++
 	xul.dll!mozilla::ipc::MessagePump::Run(0x000002ae9d887030) Line 88	C++
 	xul.dll!MessageLoop::RunInternal() Line 315	C++
 	xul.dll!MessageLoop::RunHandler() Line 309	C++
 	xul.dll!MessageLoop::Run() Line 291	C++
 	xul.dll!nsBaseAppShell::Run() Line 139	C++
 	xul.dll!nsAppShell::Run() Line 412	C++
 	xul.dll!nsAppStartup::Run() Line 276	C++
 	xul.dll!XREMain::XRE_mainRun() Line 4639	C++
 	xul.dll!XREMain::XRE_main(4, 0x000002ae9d8020a0, {...}) Line 4774	C++
 	xul.dll!XRE_main(4, 0x000002ae9d8020a0, {...}) Line 4855	C++
 	xul.dll!mozilla::BootstrapImpl::XRE_main(4, 0x000002ae9d8020a0, {...}) Line 45	C++
 	firefox.exe!do_main(4, 0x000002ae9d8020a0, 0x000002ae9d536be0) Line 213	C++
 	firefox.exe!NS_internal_main(4, 0x000002ae9d8020a0, 0x000002ae9d536be0) Line 295	C++
 	firefox.exe!wmain(4, 0x000002ae9d52e4c0) Line 131	C++
 	firefox.exe!__scrt_common_main_seh() Line 288	C++
 	kernel32.dll!BaseThreadInitThunk()	Unknown
 	ntdll.dll!RtlUserThreadStart()	Unknown

This doesn't block secure-proxy-mvp, because we Exclude also http://detectportal.firefox.com/success.txt?ipv4 and *6 · Issue #123 · mozilla/secure-proxy in the addon.

I'd like to point out that I am seeing this crash a lot, and it is making it hard to test the modifications I am making to support secure-proxy, because I need to ensure these modifications don't break proxy in the general case.

Assertion was removed in bug 1557292