Absolutely. Having the tab placement customizable is something I miss from the Opera.
[1] https://addons.mozilla.org/firefox/addon/tree-style-tab/
> I want a simple vertical tab, without tree features.
> Vertical Tabs (https://addons.mozilla.org/firefox/addon/108862/), VertTabbar (https://addons.mozilla.org/firefox/addon/8045) or Vertigo (https://addons.mozilla.org/firefox/addon/1343) can do it.
Tree Style Tab has lots of bugs for me, like permanently hiding the navigation bar after I exit full-screen, and scrolling all the way to the bottom of the tab list whenever I restore a closed tab. I still use it because I love being able to organize my tabs hierarchically, but if someone only wants vertical tabs, they should choose a simpler add-on that is less likely to have bugs.