I used Bookmarks Sync and Sort for a while with my Firefox 2, but after upgrading to Firefox 3 it wasn’t available anymore and the development seems to be discontinued.
I thought about fixing the problems myself and dig into the Firefox extension development, but luckily I found SyncPlaces.
This extension allows you to transfer you bookmarks to any FTP- or WebDAV-enabled server as XBEL, JSON or plain HTML file. This is that useful you might comment, but it can merge the files before uploading it.
This is very convenient if you often use different machines, e.g. at work and at home, and want to keep your bookmarks in sync. Of course, there are other, public services, but I’d prefer to keep that private. This seems to be an intention of the SyncPlaces developers as well and you’re able to encrypt your stored bookmarks.
Last, but not least, I’d like to mention the automation option. It allows you to do the task of merging and uploading your bookmarks on a regular basis and not only at start and shutdown of your Firefox. Very nice, indeed.