You are browsing the web. You liked a url and wanted to share it, probably on twitter.
The old lengthy way:
You will open twitter.com, login with you username and password. Open url shortner like bit.ly and shorten the url you want to share. Then post your tweet with some text and shortened url.
The new and quick way:
You can do the same very easily and quickly. I hope you are using Firefox. So, there is a firefox addon Shorten url which will shorten the url and display the result in location bar. It supports more than 100 URL shorteners.
You can always remain logged in in twitter with the firefox addon Echofon. Echofon adds a tiny status bar icon that notifies you when your friends post tweets. You can also view updates in a timeline and post your own tweets.