Edit: After half day, my wife’s Mac started having the same problem. I have then applied the solution that I found in the Apple
Instagram Launches Full Web Interface Including Your Feed
Over the last few months we have seen Instagram focusing on its web interface which was none existent this time last year. Today they introduced their new web interface for desktop browsers which allows users to see their full newsfeed.
The update allows users to comment on photos and also like other users images online just incase you do not have your iOS device with you. It is worth noting that you can not upload images to Instagram via a desktop browser this still requires a mobile device.
It is impossible to tell but it is certainly looking like since Instagram were acquired by Facebook for $1 billion back in April 2013 it seems as they have focused a lot more on the users web interface which all users should be able to access today at Instagram.com