Importing Bookmarks
If you have previously used a different browser or want to e.g. import your bookmarks from a memory stick or other media, Bookmark Manager's Import function is what you are looking for.
*mozilla.gunnars.net/img/ff_bookmark_import1.png
To open Import, select File -> Import in Firefox's Bookmark Manager window.
*mozilla.gunnars.net/img/ff_bookmarks_import_2.png
A new window will appear, asking you where you want to import your bookmarks from. If you want to import your IE favorites, or if you want to import bookmarks from a Mozilla Suite or Netscape 6/7 profile, select the appropriate option. Firefox will automatically find and import your favorites/bookmarks for you.
If you want to import bookmarks from another browser, backed up Firefox bookmarks, or bookmarks from any other source, select From File. In this case, a dialog window will appear that allows you to select the file you wish to import. Please note that it may be necessary to export your bookmarks first, depending on the browser you want to import them from.
Source: *mozilla.gunnars.net/firefox_bookmarks_tutorial.html