Another Twitter feature that was previously filled by third parties is short URLs.

Expand Short URL does the same task as another Firefox add-in, Long URL Please.

Short URLs seem a necessary evil at this particular moment in the web's history.

The free Firefox add-in Expand Short URL does an excellent job of solving the problem.

You get redirected to the short URL, so you can grab it and copy it.

Expand Short URL works on all Web pages, including Web mail services and social networking sites.

Right-click any short URL and select Expand Link, and a box pops up, showing you the original, long link.

Still, if nothing else, Tr.im serves as cautionary tale for anyone interested in creating archival short URLs -do it yourself.

Now, when you create a post on your WordPress.com blog, you'll see an option to create a short URLs using the new wp.me domain.

While not entirely solving URL-shortening issues like link rot, Tr.im appears poised to at least become a bit like the Mozilla of short URLs.

Su.pr also plans to offer custom short URLs as well as "SEO friendly" URLs, giving you the option to avoid the StumbleUpon toolbar entirely.