Another standard feature that Opera is missing is support for middle-clicking an item in the bookmarks menu to open it in a new tab.
Firefox, Safari and Chrome all support this.
After years of waiting, Opera finally implemented right-click support for the bookmarks menu. Maybe Opera will get middle-click support some time too.
The workaround for Opera is to forget about the bookmarks menu and use the bookmarks panel (as it supports middle-click) or use ctrl + left-click or use right-click and choose "open in background tab".