Want to easily add subscriptions from within Firefox? You don't really need the live bookmarks feature of Firefox? Then FeedBag is the solution.
FeedBag is a very simple Firefox 1.5+ extension that changes the live bookmark subscription icon in the URL entry to add subscriptions to Liferea instead of creating a new live bookmark subscription.
To do this FeedBag relies on DBUS to send subscription requests to Liferea. So if it stops working please check that both Firefox and Liferea are started from within a DBUS enabled environment.
You can find FeedBag on addons.mozilla.org but you can also find the XPI on the SF project page or in the source tarball.