Earlier quoted context omitted.
As you alluded to at the start of your post, Chromes speed improvements were more technical than it was due to a lack of bloat. In fact Chrome consumed more memory than FF did at that time and that was down to it being multi-processed (ie one heavy page wouldn’t slow down the rest of the application in other tabs) but that came at a cost in terms of RAM used. Obviously the v8 stuff also made a massive difference too.
Honestly, I hate the term "bloat". Most of the times when I've seen bloat blamed, the real cause has been a bad algorithm somewhere. Just as was the case with Chrome, its often the case that using more RAM (and maybe more "bloat") can make things faster.
Along the lines of a custom memory manager, that never releases memory back to the OS. If you open tons of tabs, closing them wouldn't release the memory back. Which is a decent guess - it used the memory once, it will probably need it again.