Firefox users have been annoyed by the lack of a method for importing Firefox bookmarks into Safari's Spotlight-searchable index. So I wrote a shell script that will do the import; you can schedule it to run as often as you like. Just follow these instructions, and you'll be able to search your Firefox bookmarks via Spotlight.
[robg adds: I tested the script, and it works as described...]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050825165843574