I think this is a very nice extension. I've been using Tabs Outliner before (I actually paid a one-time donation to get the full version, which was worth it for me, because this is a really important feature to me) but Sidewise seems like a good competitor. It's lacking in some parts (like backups and keyboard shortcuts), but it's innovative in others.
One thing I like is the ability to highlight tabs, but I think it needs some more colors to be truly useful.
The labels/titles are pretty good as they are, but I would like to be able to comment on empty rows too - not empty tabs, just rows with no link at all.
When you pin a tab and unpin it, it doesn't return to its original position. Being able to pin a tab to the top, and then return it to its place in the hierarchy, would make more sense and be more useful.
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