This sounds like the known bug in xulrunner: https://bugzilla.mozilla.org/show_bug.cgi?id=421482
The issue is unfixed AFAIK (long tread, hard to keep track of the status), but one of the recommendations is to set preference 'toolkit.storage.synchronous' to 0. This is DANGEROUS, as it could result in the loss of your bookmarks and history and such, but in the case of an RSS reader, do you really care? The Liferea profile is independent of Firefox's.
I'm giving it a shot on my system. My initial impressions is "HOLY CRAP THAT STARTED IN LESS THAN 2 MINUTES!!!" It actually look all of 3 seconds.