missing stylesheet in firefox

site was hacked and I started changing permissions and replacing a couple of files. Now have it working in ie, but for some reason not working in firefox. The stylesheet is missing in firefox, even though it’s there. any ideas what I can check to figure out the issue.

I changed theme/index.php and theme/header.php but also in the admin the thumbs for the themes ie: default wordpress theme are also missing.

Thanks for any help