Sometimes, a content provider will attempt to obfuscate the links to the original files, so that you can't just come along and use DownthemAll and Firefox to download all the RFAs and RVTs in one hit.
However, there is a way around this - its called iMacro, and it is also an addon for Firefox.
Basically, you can set it to record actions you take using your browser, and then replay these actions as a script. Its very powerful and gives you a lot of control.
A few little tweaks that you might want to add to the start of the script:
SET !ERRORIGNORE YES
SET !LOADCHECK NO
SET !TIMEOUT 100