You can use the bookmarklet they provide for Firefox. Just rightclick and add it to your bookmarks (I have a folder for bookmarklets). Works the same as the webclipper in Windows. You can select what you want using the mouse cursor, or clip the entire page. Either way, when you want to clip something, bring up your bookmarks and click on that bookmarklet. A small evernote window will pop up on that page allowing you to choose the folder and edit any tags and names you may want.