If you only want to synchronise between IE and Firefox on one computer you can use a Firefox plugin called PlainOldFavorites.
With this plugin installed you can use the normal IE/Windows favorites from within Firefox.
Use a service like google bookmarks or delicous to manage and store the bookmarks online. they offer a bookmarklet for your web browsers to have easy access for storing and retrieving your bookmarks.This is not as clean as an browser-integrated solution, but it works.
Xmarks (www.xmarks.com) enables bookmark synchronization for different web browsers. Once it is installed, it makes backups of and synchronizes the users bookmarks. It is accessible through the web, so that bookmarks can be used and managed from everywhere, without the need to be at your home pc.