Need help to instruct Arduino log in username for browser

Hi I'm new to programming. How to instruct Arduino to interact with browser ( say Firefox,IE) to automatically log in to my favorite website ( yahoo mail,facebook, gmail) when connected. (Ethernet connection). Means, web browser will send URL to Arduino and once the URL match with database(code) it will log on automatically otherwise it will be idling.

For security purpose i want to use thumb print to allow arduino connect to the PC after user verification. Without thumb print the arduino will not activate. Can anyone help me on this? is the any library i can make use for it? Can please guide me on this :~

How to instruct Arduino to interact with browser ( say Firefox,IE) to automatically log in to my favorite website ( yahoo mail,facebook, gmail) when connected.

In general, you can't. Sites that require logging in generally use the https protocol, rather than the http protocol. The Arduino can not support the https protocol.

I'm not entirely sure what you're trying to achieve here, but if you want the Arduino to help your PC log in to web sites then a password manager on the PC would be a better way to go IMO. If you insist on rolling your own then something like Greasemonkey would be one way to do it, but I very much doubt you actually need to reinvent your own solution.