[Greasemonkey] Binary downloads with GM_xmlhttpRequest

[Mark Pilgrim]

I'm writing a "Favicon collector" that downloads favicons and stores
them locally.  I would prefer to download the action icon data and
store it (base64'd) with GM_setValue, but when I download, I get a
string that has been munged, i.e. it is different from the actual
binary data, and window.btoa complains about invalid characters.  At
least I think that's what's going on; all I know is that it doesn't
work.  It doesn't appear to work with the built-in XMLHttpRequest
object either.  Is there a known issue with downloading binary data
with GM_xmlhttpRequest?

-- 
Cheers,
-Mark