Used with Firefox Dev build: I really enjoy this add-on. I love the premise. Stability seems iffy: (1) I sometimes observe the parent tab separated from its children, i.e. there will be tabs in between the parent and the child at inconsistent depths; (2) I have observed once in the first few hours of using it the whole sidebar becoming blank and unusable, requiring a restart. I also have one suggestion: I find that this add-on simply supersedes the vanilla browser tab strip, so it would be nice to have an option to hide the default horizontal tab strip.