goo.gl lite 1.9 works well Rated 5 out of 5 stars
and flawlessly in Firefox 13.
It is a very good seamless alternative to goo.gl URL Shortener extension for Chrome.
Question to the developer: any particular reason why the version 1.9 is not signed?
1.9 is "preliminary reviewed" as Mozilla terms it. They didn't grant fully reviewed because my add-on includes oauthorizer. Also, that add-on/resource (not the code I wrote) uses synchronous AJAX in parts. I haven't had a chance to fully discuss or address this. However, I believe the current add-on is safe to use.