I got this alert when signing in:

We noticed that you are using a non-Citi certified browser. For the best Citi Online experience, it is recommended that you use a certified browser.

I was using the latest version of Safari, version 10.1.1. So I checked the linked page, emphasis added:

You are recommended to use supported and updated browsers to ensure that your internet banking is secure.

Solid advice. What versions are supported?

Safari 7.0
Safari 8.0

Most firms I’d give the benefit of the doubt, but poor showing for a company this size, folks!

I last mentioned Citibank in 2008, for some sneaky advertising.