I just had an idea that might be usefull for Roundcube to implement. How about supporting a generated RSS feed of your email; so you can add that to your Firefox/whatever RSS reader; which will then notify you of new email? A link to /?auth=lala&_task=rss would be sufficient. We could show that link for every folder, and add a keepalive call to the RSS read action.
Bombs away :P
-- Regards, Sjon