I suspect you're using many extensions. Most users do not, at least according to FF's stats.
Process sandboxing is not a user-visible feature; it's (1) a largely hypothetical security feature (hypothetical in the sense that it's not empirically obvious that complete sandboxing is better than alternatives), (2) a means to discourage locking and make the browser snappier.
Note that by now, firefox does use process sandboxing, and indeed has used process sandboxing for the most critical bits (plugins-i.e. flash) for years. Benchmarks do not back up your claim that Firefox is a lot slower than chromium; nor is that my experience. For a long time, scrolling was smoother on firefox than on chrome - I often read long webpages in auto-scroll, and chrome was janky on some pages firefox was not - and the reverse was true too (although to this day, when it works, it never works as well on chrome as it does on FF, for some reason).
The FF developer tools have at times lacked some features, but there have also been features they've had before chrome, e.g. the rendered font display. I can't right now think of a devtools feature in chrome that I'm missing in FF. I certainly debug in both all the time.
For a very long time, font rendering on windows was better, and hi-dpi worked while it didn't on chrome.
Chrome's a good browser, and it's still snappier today. But the difference is really splitting hairs at this point. There are much larger differences in day-to-day usability that people put up with all the time. I don't buy that chrome's undeniable strengths are sufficient to be noticeable unless you're actively looking for them; and chrome also has bugs and issues other browsers don't; it's not a pure win.