> sometimes I get to a dead end and want to navigate back to where I was, but have somehow lost the thread of how I got there, either b/c I was doing cmd + click and lost the tab and / or closed it or because it's now buried in the current tab's history.

When I'm researching a subject (like general research), trying a few different approaches for search queries and keywords until I get a result page with some promising results. Opening the promising results in background tabs, but at some point I just click, when I believe it's the last promising result, which then replaces the search result page and its history of previous queries. Then I try the opened tabs, quickly scanning them, closing some if they are obviously not what I need. At some point I decide I may need some more searches, but which of the tabs again had the history with the search queries in them? Did I close it maybe? It's often easier to coax Firefox's awesomebar into revealing one of my recent searches/history and continuing from there cause trying to dig up that one tab with the history you need, at best it only takes me completely out of my flow :)