Also, del.icio.us has been growing since Yahoo acquired the company. There is a plug-in for Firefox that works quite well. I don't use it del.icio.us myself, but I hear the plug-in makes it work really quite seamlessly with Firefox.
That reminds me, one thing I've done in the past is to email the firefox bookmarks.html file to my gmail account. Pretty quick and easy. You could probably even script it since the bookmarks file is in a known location. Just drop a simple script app on your desktop and you can "synch" up whenever you like. Or use Transmit and the FTP widget to upload the file in a similar way.