great Rated 5 out of 5 stars
For firefox 16.x. Here's how:
1. Download the .xpi file to your computer.
2. The .xpi is a file like a .zip, Open it using a zip application like 7zip.com.
3. Edit the install.rdf file and change the max version to 16.0.*
4. Save, and then open with firefox to install.
I have contacted the developer to fix the above but his email address is bouncing back. I prefer CSS viewer than anything else found as CSS viewer coz it's lightweight and works like a charm without any other heavy features that a non-developer guy doesnt really need. Kudos!