Open the Bookmarks manager (press ALT on your keyboard, click Bookmarks>Show All Bookmarks), and find the bookmark(s) you want to specifically move to another Firefox. Drag the bookmarks out of the Bookmark Manager window and onto your desktop or in a folder. They'll create shortcuts. You can then move them onto a removable drive or upload them to a website (any way to move it to the other computer). On the other computer, move the shortcuts from the removable drive/download them/etc. Now open Firefox on that computer and open Bookmarks Manager. In Bookmarks Manager, go to where you want the bookmarks to be and drag the shortcuts into the Bookmarks Manager window. They'll appear as bookmarks. Unfortunately, there is NO way to move whole folders specifically from one Firefox to another.

A possibility is to use a second profile to create an HTML backup and keep both profiles open at the same time. Then you can copy bookmarks or bookmarks folders from the Library of one instance to the Library of the other instance that uses the second profile.

• http://kb.mozillazine.org/Profile_Manager
• http://kb.mozillazine.org/Creating_a_new_Firefox_profile_on_Windows

If both profiles are open at the same time then you can copy and paste selected bookmarks from the Library in the current default profile to the Library in the second profile. Start the second instance (profile) with the -no-remote command line switch to be able to have both profiles open at the same time.

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

You can export those bookmarks to an HTML file and use that file to import those bookmarks on the other computer. That is usually easier then editing a full HTML backup.

• https://developer.mozilla.org/Mozilla/Multiple_Firefox_Profiles