Firefox 3 doesn't store your bookmarks in the plain old HTML file that Firefox 2 did, so desktop launchers like Quicksilver and Launchy can't index them properly. But the HackCollege blog has a solution: a Firefox 3
about:config tweak that makes Firefox automatically export your bookmarks to a file. Change the
browser.bookmarks.autoExportHTML value from false to true to get a
bookmarks.html file saved to your Firefox profile directory each time you shut down your browser.
Indexing Firefox 3.0 Bookmarks with Quicksilver [HackCollege]