There is an experimental version for FF6 Rated 5 out of 5 stars

https://addons.mozilla.org/en-US/firefox/addon/evernote-web-clipper/versions/I can recommend looking under versions history of add-ons, they often have a experimental version available. And it works fine for me!

This review is for a previous version of the add-on (4.0.0.155231).