Uploading files to direct to S3 from another site using CORS failes if HTTPS Everywhere is installed
Version: 3.4.2 on Firefox 25
Many sites have a file upload feature that uses AWS S3's ability upload files directly to S3 using CORS. There is a jquery library that makes this easy.
If HTTPS everywhere is installed on Firefox 25 the OPTION request is never made. If HTTPS Everywhere is disabled and firefox is restarted the upload will work.