Sends only "@@" instead of generated password on VirusTotal.com

[Nokta-strigo]

I enter @@ and my master password on the new https://www.virustotal.com interface, press "Sign in", it sends POST request with such body:
{"data":{"user_id":"address@example.com","forever":false,"password":"@@"}}
If I press F2 and enter the master password, it sends:
{"data":{"user_id":"address@example.com","forever":false,"password":""}}

Firefox 55.0.1 (64-bit), Linux Mint Debian Edition.
PwdHash 2.0, Last Updated August 9, 2017
To capture the request body I use "Live HTTP headers"