Rated 5 out of 5 stars
Aside from Tab Mix Plus, this is my favorite add-on for Firefox. I'm a blogger, and I often have to copy text from web pages to paste into WordPress. As anyone who works with blogging software knows, sometimes pasting in brings over HTML formatting you don't want, and having to deal with the Paste As text thing gets tedious when you literally do this copy/paste operation 100 times a day.
The Copy As Plain Text option makes the whole thing simple and straightforward. And it's SO, SO wonderful that it comes with a keyboard shortcut. So many other extensions of this type make you use the mouse.
I also use he Copy As HTML command more than I thought I would when I first started using this add-on. Again, it's very useful when blogging or doing web design because I can see exactly what's behind how text is formatted on a page and then just strip out the bits I don't need.
If you copy text from the web a lot and find you have to keep taking the formatting out, then get this add-on. It will simplify your life.