Something similar exists in Google Chrome/Chromium. When you highlight and then right-click on a domain name (it doesn't have to be a link), a menu pops up with the option to, "Go to robotfindskitten.org".

As you have suggested, some code that would detect the presence of a URL would work well. But, to avoid confusion with following people on Twitter, I think instead of 'Follow' you should use 'follow link', 'go to' or something similar.

Best of luck,
Jack