2. TAB STACKING
This is a godsend for those of you who somehow end up with way too many tabs that you don't read anyway. Tab stacking in Vivaldi is an easy way to keep the tab bar as uncluttered – relatively at any rate – as possible. Tabs are stacked by simply dragging one tab onto another, and stacks are indicated by a series of horizontal dashes along the bottom of the tab.
Clicking these indicators lets you select individual tabs in each stack, although space constraints clearly mean that three or four tabs is probably the optimal amount for each stack.