Firefox and userContent.css problems

   Hi I've edited the userContent.css file for adblocking, from the 
Firefox tips and tricks page (http://texturizer.net/firefox/tips.html), 
and placed it in the appropriate folder ~/Profiles/default.xxx/chrome/ 
as indicated. However, it does not block any ads. I've tried putting the 
file in several places, but still no luck. I have success with the same 
userContent.css file on two Linux computers, and one Windows, with Firefox.
  Anyone else out there using OS X and Firefox having any problems? Thanks.