I believe that the recent enhancements, such as group tabs and vertical bars, are fantastic improvements! However, I feel that an important feature is still missing: a visual distinction for the nesting levels of tabs. For instance, when I create a new tab, it represents a hierarchy level of 0. If I open a link from that tab in a new one, it would then have 1 ancestor, and if I do this again, it would have 2. This concept of "nesting" is what makes extensions like "Sideberry" (https://addons.mozilla.org/en-US/firefox/addon/sidebery/) and "Tree Style Tab" (https://addons.mozilla.org/en-US/firefox/addon/tree-style-tab/) so effective and user-friendly. I suggest implementing an opt-in option that allows users to visualize the nesting levels of their tabs. This functionality could greatly enhance the user experience and organization of tabs.
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