You really do need to use Flash, AFAIK. I investigated this a while ago. Firefox has an API, but the user has to change an option to specifically allow access

You really do need to use Flash, AFAIK. I investigated this a while ago. Firefox has an API, but the user has to change an option to specifically allow access to the clipboard. In the end, I figured it wasn't worth it, and that programmatically selecting the textbox was 90% of the functionality without all the headache.