the "add friend" button doesn't do anything for me

whenever I try to add a friend, I hit the button and nothing happens, there's not even a popup

I only have 17 friends out of the 300+ possible and when I look at the console, it sends the message "error 403 (forbidden)"

any idea on how to fix this?

edit:
full console messages:

Failed to load resource: the server responded with a status of 403 (Forbidden)  
Uncaught TypeError: Cannot read property 'failed_invites_result' of undefined  
Failed to load resource: the server responded with a status of 403 (Forbidden)  

and now it's spamming:

GET http://steamcommunity.com/actions/GetNotificationCounts 403 (Forbidden)