Tree style tabs is an absolutely essential browser add on for me. I can't thank the author Piro enough for all the YEARS of keeping this up to date and now that he's even supporting Firefox 57 I'm just amazed. This feature should be a part of Firefox's core experience. It's the biggest differentiator between FF and Chrome and it's why I will open often upwards of 200 tabs (I'm not exaggerating) without issue and keep those trees of tabs open for weeks as I work through certain issues and only close them when I'm ready to move on. In fact, Tree Style Tab removes the need for Bookmarks as it saves not only the page but the trail of history that led you there. I will often Google a topic and then control click the first 6 links then go through the tabs closing the links that aren't helpful. It's a huge time saver and just works in a way that really clicks with me.