Firefox typically only automatically offers to and imports bookmarks from other browsers once, during the first ever installation of Firefox.

You can usually find the imported IE Favorites in a folder ("From Internet Explorer") at the bottom of the Bookmarks Menu folder (Bookmarks > Show All Bookmarks).

If you can't find them in the "From Internet Explorer" folder then try this:

Export the Favorites in IE to an HTML file and import that file in the Firefox Bookmarks Manager.
That way you also preserve any sorting that you may have done in IE with the Favorites.

• Export the favorites in IE to an HTML file (bookmarks.html): File > Import and Export
• Import the HTML file in Firefox: Bookmarks > Show All Bookmarks > Import & Backup > Import HTML: From File

See also:

• http://kb.mozillazine.org/Import_bookmarks ("Import from another browser" and "Import from file")