Opera 9
Safari 5 Mac (pre validation nerf)
Firefox 4b12
Mobile Safari (iOS 3.1) Keyboard
IE 10 Platform Preview 2
The Low Down
Opera 9 styles the input with an url icon.
Safari 5 (Windows) and Chrome 6 will focus the input upon submission with invalid data, but no message shown.
Mobile Safari does no validation, but brings up a keyboard which features an [/] and [.com] key and not a space key.
Name attribute is required for validation of value.
Firefox 4-6 has pretty loose validation (e.g. "a:" will validate)
Opera 11 will add "http://" to "abc" making "http://abc" as form input data. Characters generally not
allowed in URL's will not go through though (e.g. "*"). Need to test: unicode URLs.
Chrome 6-9 accepted attribute but didn't validate until 10.