Sorting and rearranging bookmarks - Firefox
From MozillaZine Knowledge Base
Mozilla Bookmark Sorter is a graphical Java program which alphabetically sorts Firefox/Mozilla/Netscape formatted bookmark files (usually called bookmarks.html). Here are the installation and usage instructions.
Another option is to use Sort Bookmarks, a Firefox-only extension.
Alternatively, you can right-click a folder and select "Sort by Name" (in recent versions of Firefox only).