Type chrome://net-internals/#hsts in the address bar of chrome
Query domain: if it appears as a result, it is HSTS enabled
Open file explorer
Copy paste %APPDATA%\Mozilla\Firefox\Profiles\ in the address bar of file explorer (for Linux it is ~/.mozilla/firefox)
Double click the folder you see (if you have multiple FF profiles, there will be multiple folders)
Open SiteSecurityServiceState.txt. This textfile contains sites that have enabled HSTS.