There are some browser extensions out there which allows to preview the original URLs in sites like Twitter,  an extension like Long URL Please automatically turns short URL on pages into original ones,  Unshorten Opera extension is similar to Long URL Please automatically converts short URLs into original URLs.

unshorten Opera extension changes short URLs to original ones

Unshorten extension looks for shortened URLs on pages, if it finds any automatically changes shortened URL to original by making requests in the background to find real target URLs.

Unshorten can be configured to rewrite URLs to originals, add a title attribute with original URL and replace URL string to the original.

Unshorten Opera extension