Getting RAR files to auto save in Firefox

I was stuck with this problem for a while, and I never understood why it ever came to be, but if you download a '.rar' file in Firefox, you will always get prompted as to what to do with the file. If you select 'download', the checkbox to remember the action remains greyed out, and you get a prompt every time. This is inconvenient if you have a series of files to download, for example if there is a file split into, say, ten rar files: file.rar.part1, file.rar.part2 and so on...

This solution works on a Mac, but should also work on Windows, albeit a little common sense tweaking might be required.

Look for you Firefox 'mimeTypes.rdf' file. This should be located in:

/Library/Application Support/Firefox

Edit this file with a pure text editor, I use TextMate (Windows users Notepad will be fine). Then add the following (making sure that it is pasted between the end of another RDF description, so look for a tag, create a new line and paste away...):

<RDF:Description RDF:about="urn:mimetype:handler:application/rar"
NC:saveToDisk="true"
NC:alwaysAsk="false" />
<RDF:Description RDF:about="urn:scheme:mms"
NC:value="mms">
<NC:handlerProp RDF:resource="urn:scheme:handler:mms"/>
</RDF:Description>

Also, and not sure about how important this is, look for the section that starts:

<RDF:Seq RDF:about="urn:mimetypes:root">

and add another line within that tag:

<RDF:li RDF:resource="urn:mimetype:application/rar"/>