I have customized my bookmarks so that I don't need the bookmarks (BM) toolbar to be visible. All of my BM have been put into one self-titled folder and that folder has been moved, through the customization menu, from the BM toolbar to the Navigation Toolbar. I keep it just to the right of the URL, Refresh Button, and Close Button. To the right of BM is my adblockplus and greesemonkey buttons which never disappear. Only the BM folder will disappear. In addition to this placement, I can hide the BM toolbar (BM folder remains). When I close FF there's no errors or anything but when I reopen, the BM folder is again gone. The only remedy, annoying as it is, is to reopen the BM toolbar which will then show my BM folder in the Nav Toolbar.