So what is Two-Level Tab Stacks? Do you group and manage tabs in Tab Stacks? We’ve had Tab Stacks forever, but now we take this awesome feature to the next level, literally. In the new version, you can display stacked tabs on a second level in the Tab Bar. �� Better display, more control Two-Level Tab Stacks are great if you want to display stacked tabs in full size. The feature offers all the other benefits of normal-sized tabs and works perfectly with tabs at the top, bottom, or to the side. Choose between Two-Level Tab Stacks and Compact Stacks.