Love the grouping feature and that I can close individual tabs with their own [x] button without having to first navigate to them.

Some ideas:
- Visually maybe it would be best to show each tab's [x] button on hover though
- Should be able to drag left to ungroup (unindent) one level and drag right to group under the previous (above) item
- Also, it would be really if a filter box was on the top to select which tabs to show (filter titles using typed substring). Indentations should be remembered (that is have invisible parents if those are filtered out). If hard to implement, it could at least highlight found items or gray out items not found. Could also have that as option and could have Previous/Next button to select next tab that matches the filter