Yes, the places database (history, bookmarks, etc.) can get pretty big. Comparisons should be made with the same profile on both.
Absolutely. To each their own. I've seen my browser eat as much as 8GB of RAM. I browse the web in a breadth-first fashion rather than a depth-first option. I rarely click on links; I almost always middle-click on a link. I also made an addon that lets me middle-click on form submission buttons so forms are submitted as new tabs (actually really useful). The end result, after a year or two of use, is a gradual buildup of tabs (it's not like I opened all of them in a single session).
Yes, I'm quite partial to Firefox and am upfront about it. So what? At least my posts are coherent (we're talking about browsers, not OSes, and I won't even try to take a stab at whatever the heck you meant by Sierra Nevada).
Pale Moon adopts the changes that Firefox adopts and only diverge in ways that don't involve much, if any, change to the source. Take, for example, killing the old (and arguably more useful) "Toolkit" download manager? That happened on Firefox (and not everyone was happy about it), and it happened on Pale Moon. The addon/extension system exists in Firefox to let users change the UX experience, because not everyone is going to agree on what the best UX design is; I'm not happy with the way Firefox works out of the box, and I don't see Pale Moon as being any better.
I'm not saying that PM is bad (it is the easiest way to get 64-bit support without resorting to nightlies), and the fact that it is basically Firefox with tweaks on the periphery means that it's just as good. If they want to recompile and repackage Firefox, sure, go ahead. I won't mind having a 64-bit build not based on a nightly. But don't try to pass it off as something much more different that is rebelling against the clueless idiots at Mozilla; if they really think that poorly of the code, why the heck are they using it?