1) You will have to monitor clipboard activity
]. As I see, you will have to use P/Invoke, since there are no tool for that in the framework.
On every detected change you have to do following:
2) check the content of the clipboard for text format
3) get the active window and check if it is a browser - you could omit this constraint
3) validate the text from the clipboard for url syntax
4) give the value to the textbox