Hi there
Open up opera and click on the top left Menu Button (Opera button). Select the option Bookmarks > Manage Bookmarks Once the window has opened up, from the menu select File > Export as HTML and choose a suitable location to save them too. Now close Opera.
Open Firefox. From the bookmarks button (Top Right) Select the option Show all book marks (or press ctrl/shift & b) Now choose the option Import and Backup and select Import bookmarks from HTML. Now navigate to the file we exported from Opera and choose the OK button and your bookmarks should now import from Firefox to Opera.
Hope this helps