SyncPlaces is a Firefox extension that allows you to synchronise your bookmarks and passwords between different installations of Firefox (e.g. a browser at Home and another at Work), and also to sort your bookmarks. It only works with Firefox v3 and above (but is compatible with older bookmark extensions). The synchronize feature requires your own Web or FTP server, which is used to store the bookmarks centrally, but there are a number of free servers you can safely use (see the Support section for details of at least one of these).
Using your own server means you get to keep you bookmarks private rather than storing them on a third party server who may analyse, probe and profile you, sell that data to others, or use it for their own nefarious purposes ;)
If you just wish to sort your bookmarks then you probably just want the SortPlaces extension instead. This is one of a number of extensions I've written that you may find useful.
Bookmark synchronizer that keeps your bookmarks private by using your own web (requires WebDAV) or ftp server. Takes a backup of your current bookmarks before downloading, which you can restore if it all goes wrong. You can also manually take a backup at any time, or restore from this backup.
* Support for profiles, so can now quickly change between several profiles, e.g. Home and Work. See documentation for details.
* Export/Import facility for profiles so they can easily shared
* Added Spanish locale
* Added sort options for Unfiled bookmarks
* Can now set the delay when automatically sorting/syncing
* The default delay has been increased from 5 to 30 seconds
* You can now set 'Sort order' separately for menu, toolbar and unfiled
* BUG FIX: Sorting by description and by keyword was not working
* BUG FIX: When 'unsorted' was selected for the first 'sort by' it was still sorting using the 'Sort order'
* BUG FIX: XBEL Import/Receive did not always work when synchronising a folder

The license of this software is Free Trial Software, you can free download and get a free trial before you buy. If you want to get a full or nolimited version of SyncPlaces, you can buy this browser plug-ins software software.