Configure Account returns could not get balance for unlocked custom accounts

[donfrigo]

Potentially only happens in Live environment

Description
Configure Account returns "could not get balance from custom account", even when network is set to Custom.

Steps to reproduce
Requires a local Ethereum node running at localhost:8545 and a given wallet mnemonic.

1. Click the Select a Network button
2. Edit the Default account
3. Select custom
4. Click Unlock
5. Paste in the wallet mnemonic and confirm with OK

Observed output
Browser console output returns:

Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://localhost:8545/. (Reason: CORS request did not succeed).2

Firefox version 69.0.3

(ES-19)