There are more ways to open bookmarks in Vivaldi than can be counted on one hand. One way is to type the bookmark nickname, instead of the long bookmark link, either in the address field on the Address Bar or in Quick Commands.

To give your bookmark a nickname, edit the bookmark and type a word you associate with the bookmark in the Nickname field.

Then, whenever you want to open the bookmarked page, just type the nickname in the address field or Quick Commands and press Enter. While typing, you can also see matching nicknames and the link they’re for in the drop down menu.

In Quick Commands, to open bookmarks as soon as you’ve finished typing their nickname, you can enable “Open Bookmarks on Nickname Match” in Settings > Quick Commands > Quick Command Options. That way you can even skip pressing Enter.