That is a plugin for working with c2m services(http://index01d.com/c2m/). This plugin allows you to share your code with cc2m(copy code) and substitute long urls to short ones with cu2m(copy url). Plugin puts url to code or short url into clipboard.
This add-on has been preliminarily reviewed by Mozilla. Learn more
This add-on is not compatible with your version of Firefox because of the following: