Reinstalling Safari 10 may be an option, but if you haven't got the installer archived there's no way I'm aware of to do it.

Maybe try deleting the site from Safari > Preferences > Passwords and shutting down/starting up before trying the site again.

The new Great Equalizer is the SEND button.

In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire