I, as many other WordPress users, have encountered a problem with Full Text Feeds not actually showing on FireFox Live Bookmarks (the thingy that shows you the feed in a nice way) as full text, but are rather cut.
It seems this is not a problem at all. This is a feature in FireFox’s Live Bookmarks which simply shortens the text only on display. If you’ll look at the page source (View -> Page Source) you’ll the see the XML file of the feed and that the <description> tag contains the full text.
It seems IE7 doesn’t do that and shows whatever it is it needs to show.
Don’t be alarmed by this, your WordPress blog DOES show full text feeds.
If you really want to test this, go to a full blown RSS reader and put your feed’s URL and see that it does contain the full text.