How to copy selected text from other website to a window opened from my website

I am opening a new window that has a small form from my website. This is like a keyword submitting form.

People can search in different article website and submit keywords there.

I need a functionality where users can goto any website and hightlight the text they want to copy and this should be auto-filled in the keyword field in that window of my website

Is i开发者_JAVA技巧t something possible?

Should be possible if you like building browser plugins :)

Firefox addons developer guide

Google Chrome Extensions Developers Guide