Event though Mozilla/FireFox will import IE6 Favorites for the first time you run them. Maybe later you add some favorites in your IE and you want to re-import the IE6 Favorites. Mozilla/FireFox do not give such re-importing IE6 favorites options but importing *.html bookmark file. So you can re-import following these steps:

1. In IE(6) goto "File" then "Import/Export..."

2. Save the bookmark URL to somewhere you can remember.(can do cookies too)

3. In Mozilla goto "Bookmarks" pull-down menu, then "Manage Bookmarks".

4. In the Bookmark Manager goto File then Import and browse to the file you saved earlier.

Reference: http://forums.mozillanews.org/index.php?board=4;action=display;threadid=346