First, start your old Firefox profile using the profile manager. The,n save the bookmarks stored there into a file:

1. menu "Bookmarks"
2. "Organize Bookmarks..."
3. "Import and Backup"
4. "Export HTML..."

After that, close Firefox and start JonDoFox, also using the profile manager. Then load the saved file the in the same steps as above, this time by choosing "Import HTML...", however.