Signing with localhost:12537 inexplicably changes txns from net999 to net2999 (?)

Describe the bug When I attempt to sign & send a transaction using the built-in network settings for Localhost 12537, after clicking "confirm", it fails to sign the transaction with an error about "net2999", even though the to/from addresses in my transaction are both "net999".

To Reproduce

Run a conflux devnet on localhost:12537 with netId 999
Fund an account and add that account to Conflux Portal
Open this html in a browser with ConfluxPortal installed:

<html>
<head>
<script type="text/javascript">
async function transfer(from, to, value) {
  value = '0x' + BigInt(value).toString(16)
  console.log({from, to, value});
  return new Promise((resolve, reject) => {
    conflux.sendAsync({
      method: 'cfx_sendTransaction',
      params: [{from, to, value}],
      from,
      value,
    }, (err, data) => {
      if (err) { reject(err); } else { resolve(data); }
    })
  });
}

async function go () {
  const from = (await conflux.enable())[0];
  const to = document.getElementById('to').value || from; // default: send to self
  const amt = parseInt(document.getElementById('amt').value) || 10; // CFX
  const value = amt + '0'.repeat(18); // Drip

  await transfer(from, to, value);
}
</script>
</head>
<body>
  <input id="amt" type="number" value=10 style="width: 3em" /> CFX
  to <input id="to" placeholder="paste address here" />
  <button onClick="go()">Send</button>
</body>
</html>

Choose "Localhost 12537" from the ConfluxPortal network options
Select any address that you want to send devnet CFX to
Click "Send"
Choose the address to send from, if prompted
Click "Confirm" from the ConfluxPortal dialogue

Expected behavior sendAsync should transfer the funds on the devnet running at localhost:12537. (It works on TestNet.)

Browser details (please complete the following information):

OS: macOS Big Sur
Browser: Firefox 89.0.2
ConfluxPortal Version: 0.6.8

Additional context

Sometimes it will not let you click Confirm, claiming that there is no balance (even on accounts with a balance on your localhost devnet.) Other times, it will fail with the following error:

ConfluxPortal - RPC Error: Error: [ethjs-query] while formatting outputs from RPC '{"value":{"code":-32603,"message":"Invalid parameters: address","data":"\"network prefix unexpected: ours net999, got net2999\"","stack":"Error: Invalid parameters: address\n    at s (chrome-extension://opafkgfpaamecojfkaialabagfofilmg/background.js:1:398023)\n    at Object.internal (chrome-extension://opafkgfpaamecojfkaialabagfofilmg/background.js:1:398412)\n    at l (chrome-extension://opafkgfpaamecojfkaialabagfofilmg/background.js:1:393516)\n    at chrome-extension://opafkgfpaamecojfkaialabagfofilmg/background.js:1:392727"}}'

This is nonsense. See the output of the console.log included in the html snippet above, which will indicate that the transaction being sent is for net999 as it should be.

Conflux-Chain / conflux-portal

Signing with localhost:12537 inexplicably changes txns from net999 to net2999 (?) #352