Try Microsoft Edge
A fast and secure browser that's designed for Windows 10
Earlier today (August 13), the Single Sign-On (SSO) protocol that is used in Microsoft Azure Active Directory (Azure AD) was updated, which unfortunately caused the SSO implementation in Microsoft Dynamics NAV 2013 R2 to fail. As a result, users cannot not log into Microsoft Dynamics NAV using their Office 365 credentials.
We are working very actively on a solution, and we fully expect to make a hotfix available for download Thursday, August 14 2014. We will update this blog post as soon as the hotfix is available.