I'm using Opera v25 developer which sounds like it may have similar bookmark functionality to v24 (but I don't know not having installed 24). Anyway here's a thread I started with my frustrations (main ones) with the latest version of Opera. You'll see I too lament the lack of reverse compatibility between the latest format of bookmarks with the earlier .adr format. Non-existent or limited bookmark storage & management in the latest versions of Opera is a huge oversight by the developers in my opinion. The only easy way I could find to make my extensive list of bookmarks available to v25 was to bookmark to an htm backup of my earlier bookmarks stored on my local drive.