If there are problems with importing the IE Favorites in Firefox then export the favorites in IE to an HTML file and import that file in the Firefox Bookmarks Manager.

If you do not have the menu bar in IE then right-click the toolbar at the top to enable the Menu Bar.

• 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 Bookmarks from HTML

See "Import from another browser" and "Import from file":

• http://kb.mozillazine.org/Import_bookmarks

Foxfire appears to import only the first ten of my IE favorite folders, in alphabetical order. I managed to import 15 additional folders as follows:

1. In IE, create new folders named a, aa, aaa, etc. and copy all the other favorite folders into those folders. Or you may group your IE favorites in folders like, A-D, E-H, etc.
2. In Firefox, click Show All Favorites, Import and Backup, Import Data from Another Browser, Select IE, Next, check only Favorites. This should import folders alphabetically.
3. Then, you can organize your Firefox favorites by dragging subfolders out of a, aa, etc. and into the "Bookmarks Menu" folder, or leave them in folders like, A-D, E-H, etc. Delete extra copies.

Importing IE Favorites might fail if the folder structure is nested too deep and the file path may get too large or otherwise has special characters.
Exporting the Favorites in IE and importing this file in Firefox usually works to get all IE Favorites in Firefox.