I've been getting that error for the last few months. Log in and the popup saying the addin MUST be installed. Download, install and just get a spinning circle. I've done it at work (IT security firm) on FF, Chrome, IE. Have tried on my personal macbook on Safari, and at home on my Win7 pc with FF, Chrome and IE.
Basically, that makes the site completely un-usable. There is no way to use MYDlink.com.
In my opinion, this isn't a trivial issue. It's a vital part of the product offering.