My blog had this vexing problem where it used to render ugly, really ugly, as the stylesheet wasn't being loaded on Firefox. However after a refresh everything was fine. Even the Alexa thumbnail displayed the front page in all its css-less ugliness. Initially I thought it was a temporary file loading error. I also reduced the number of Javascripts on the page. None of them could solve the problem. Finally today, when I was debugging a project using Firebug, I noticed the actual problem.

The stylesheet was not being loaded simply because the file type returned by the web server was text/plain instead of the required type - text/css. The solution was simple. I added the following to httpd.conf and restarted the server:
AddType text/css .css - The solution here doesn't work because the problem is elsewhere, with mod_cache.
The temporary solution is to add the style.css to DisableCache directive in the virtual host configuration section (or in the main section). The permanent solution is to update Apache. This is a documented mod_cache defect.

Thanks to Firebug for helping me solve this problem.

Note: Internet Explorer did render fine even with this error.