When Firefox's bookmarks are a scattered mess of links, you can restore order instantaneously by alphabetising them. Simply reordering the column in the Bookmarks Manager won't do it though—you've got to invoke the context menu. Macworld explains:
Select a folder full of bookmarks in the left pane of the Bookmarks Manager window. The right pane will fill with that folder's contents. If you want to sort all the items in the right pane by name, just Control-click (Ed: Windows users, right-click) on an item in the right pane and choose Sort By Name from the contextual menu. Firefox will first organise folders alphabetically, and then follow those folders with alphabetised items that carry URLs.
If you're a heavy bookmarks user, your newly alphabetised list will be a lot easier to navigate.