Works, now ! Rated 5 out of 5 stars

As the developer's response to my last comment stated, failure may have been due to several factors. With the same url as previously tested, the link was successfully shortened. Other servers do as well, an advantage here is that the resolution page displays WOT stats for the unshortened url, and this is a very good point I believe. It takes slightly longer to resolve the link because of call to WOT, I guess.

This review is for a previous version of the add-on (1.0.1-signed.1-signed). 

Did not work : example Rated 2 out of 5 stars

Did not resolve following easy shortened link :
Not a reliable extension a this time, but as mentioned, still experimental

This review is for a previous version of the add-on (1.0.1-signed.1-signed). 

I'm sorry that you have had a problem with our service. The problem seems to have been caused by an unresponsive server either on our end or's end. To hopefully resolve this I have changed our system so that in the event of it failing to unshorten a URL, it will retry once - This should hopefully allow your request to go through automatically.