I can't add second e-mail for my account in preferencies. It's write - not valid e-mail, may be wrong e-mail

What email provider are we talking about?

I will write some e-mail.providers. It a google with e-mail @gmail.com, and @yandex.ru, @mail.ru, and even e-mail my site. For every provider - the same problem. I think, may be a problem with browser? My firefox on ubuntu system... I'll try reboot on windows now and try change e-mail on windows

This not working for browser in Windows to. Some strange...