How can GMail be expanded?

Question

I would like to write a gmail extension that would add a button on an email page (or in seclectbox or something else). For information, the goal is to add a task to my task manager from email content.

What would it be? Greasemonkey script is not an option, as I would like to do this for Chrome as well.

I don’t know where to start.

Thanks for any pointers, Michael;

Answer 1

, Greasemonkey Chrome. ( FF, Chrome), "Google Redesigned" - FF.