Rated 5 out of 5 stars

Bug. 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.
To fix that bug edit the part in the twisty.css:
.tabbrowser-tabs[treestyletab-twisty-style="retro"][treestyletab-mode="horizontal"][treestyletab-allow-subtree-collapse="true"][treestyletab-tabs-indented="true"] .tabbrowser-tab[treestyletab-children]:not([pinned="true"]) .tab-icon , .tabbrowser-tabs[treestyletab-twisty-style="retro"][treestyletab-mode="horizontal"]:not([treestyletab-tabs-indented="true"]) .tabbrowser-tab[treestyletab-children][treestyletab-nest="0"]:not([pinned="true"]) .tab-icon { margin-left: 16px;}

This review is for a previous version of the add-on (0.11.2011021901.1-signed).  This user has 3 previous reviews of this add-on.