Rated 4 out of 5 stars
I tested version 1.5.7 of this extension with Firefox 22.214.171.124 on Ubuntu Linux 7.10.
The transformation works well and fast with both the built in xslt and the Saxon one, although be aware that you'll need to have the java plugin installed for saxon to work. This should be made more clear in the documentation.
The extension is intuitive and easy to use and does exactly what it says it will do. I did not notice any errors or warnings in the error console.
Minor usability annoyances: Red color in menu item and button texts that end with a question mark.
All in all, a solid and useful extension.