For those who LOVE this addon and want to activate it in FF4:
- Download the XPI (right click in the button "Add to FF" -yes, even if the button is deactivated in FF4- and save)
- Open the XPI file with 7Zip (you can use other decompressor if you want).
- In the compressed archive, edit the "install.rdf" file. (A text editor as notepad is enough).
Find the line (L.18) with this sentence: "3.0.*" and change "3.0.+" to "4.0.+".
- Update the compressed file.
- Install the edited XPI file stored in your pc, restart FF4 and that's all!
- After the restart (FF), click on the buttons bar and "Customize" it. Find CSSViewer at the end of the list.
I have been using this addon with this manual modification with no problems. Maybe you can find a bug, but I don't think so.
Kind regards from Argentina.