Script Summary: Punch through shortened URLs, to unpack the link target.
This script detects a host of of url shortener services, and will convert links like http://bit.ly/19SK5C to the real unpacked targets -- https://addons.mozilla.org/en-US/firefox/addon/10050, in this case -- so you can see where a link goes by hovering it, as usual, before clicking to actually navigate there (having no idea of even on which domain you would end up).
When the link content is the same as the link url (as is usually the case on, for instance, Twitter), the link text is also changed to reflect the actual target -- so reloading this page after script installation will show two addons.mozilla.org links. Hovering any link that was translated this way will show you which URL shortening service the original link came from, and which domain it goes to as a tooltip, i e "bit.ly => addons.mozilla.org" in this case.
If you liked this script and want to make its author happy: feel free to download, try out and review the linked extension (MashLogic), which would help getting it through the somewhat sluggish machinery of addons.mozilla.org. Thanks!