ArchView is a firefox plugin which will help you see the content of a archive file like zip, rar or iso before downloading.
from the Web Site
ArchView is an extension of Firefox. It can open archive file online and get the catalog. It also can preview or download files in archive. Currently, it support ZIP, RAR archives and ISO-9660 CD images. The most fancy feature of ArchView is that it can open an individal file without download the whole archive, since it only fetch the necessary portion. So it's suitable for checking the content of archive before download. ArchView can support HTTP and FTP protocols. It can also handle local files via file: protocol.