Note: For Firefox with Greasemonkey installed. TinyURLs and kin are great for packing links into small spaces, but not so great at revealing where the link will take you. Remove the mystery with TinyURL Decoder.
Tiny Decoder is a Greasemonkey script with seamless integration. When the script is active, compacted URLs from 13 URL shrinking services are automatically converted to their source URLs. No resource hogging extensions or bookmarklets you have to interact with, just automatic and seamless replacement. TinyURL Decoder is a free Greasemonkey user script and works wherever Firefox does.