Rated 5 out of 5 stars

Bug 1. The "tree twisties" (or just a +/- buttons at parental tab) are only shown for the top-level parent, if the tab toolbar on top from content-area. Parental tabs of lower levels don't get such the icons, though they reserve a space for it (favicon and tab's title get moved). The reserved space is also not clickable.I can manually fix this issue by editing styles inside the *.xpi, but I don't want to do that every time a new version of TST comes out.
Bug 2. There is an option "When a tab gets focus, expand it's tree and collapse others automatically". But it works only if you have trees, and if you select a top-level tab that has no children - the previously opened tab-tree won't get collapsed. Though, I think, it should. Maybe it's worth adding this as a separate sub-option. E.g. single tabs, as they don't belong to the previously viewed tab-tree, they should be treated like tab-trees, it doesn't matter that they have 0 children.

You ignore these bugs from version to version.

This review is for a previous version of the add-on (0.11.2011021901.1-signed).  This user has other reviews of this add-on.