I had the same problem using a local apache server. This solved my problem:
http://www.ifusio.com/blog/firefox-issue-with-twitter-bootstrap-glyphicons
For Amazon s3 you need to edit your CORS configuration.:
<CORSConfiguration> <CORSRule> <AllowedOrigin>*</AllowedOrigin> <AllowedMethod>GET</AllowedMethod> <MaxAgeSeconds>3000</MaxAgeSeconds> <AllowedHeader>Authorization</AllowedHeader> </CORSRule> </CORSConfiguration>