To reproduce:
Open Firefox on Linux (with or without content blocking enabled), no addons.
Type in any syntactically correct email.
Type in anything in password field.
Click "Log In"
Expected result:
Logged in.
Actual result:
Nothing happens.
Console gives the error
*Unhandled promise rejection TypeError: "NetworkError when attempting to fetch resource."*
Full console output is in screenshot attached.
Duplicate of WEB-1349. This can be the result of VPN and Proxy services, as well as hosts file tampering.