To me it's not Firefox, but I use adblock and noscript to block a lot of the stuff eating up CPU and RAM....to me it's more of a "state of the web" thing. That's why I still can surf on a Linux equipped ThinkPad T61 comfortably enough.
It used to be, when you opened a website, only one URL was being opened - the one for the page of which you were visiting. The HTML Code fit in minor kilobytes of space, and there were no scripts running pulling from other web-facing resources. And if they were, you were probably on some porn or warez site.
Today, every major website tends to have so much crap loading at once it's ridiculous. A major inappropriate allocation of resources for things that should not take them up so much. So I need 256M of my RAM to be taken up by one site because I'm not just pulling web20bullshit.com, but I'm attempting to pull stupidzone.com, google ad services, eaturmemorytoday.com, cachedadsco.io, fazbearentads.cdn, salesforce.info, buyitnow.2dy, sell2u.com, onthebrinkofinsanity.net....and all of these are pulling scripted ads, videos, and other crap embedded into the website - what we used to call "hotlinking" IIRC....and it's bloody annoying. Looking at the news? Look at Washington POst or Wallstreet Journal too much? You get a nice paywall promising a subscription. I get that these people want to make money, and like Sally STruthers said in the 80's "Sure we all do", but the way they are going about it makes me want to just turn around and say "you know what, forget this site".
About the only places I really trust on the web to be just that one thing are here (Vogons), VCFED, wiki.preterhuman.net, neocities.org, and a handful of others, because when I look in noscript, I don't see 20 things being pulled by the site after the main URL has loaded.
Sometimes, when I want to view something mainstream or heavily scripted I uend up using Links on the 486 because it breaks all that crap and only loads the main site, especially if I want to just read whats on the page and don't care about pictures, or want to just download the file. That's a whose second, practical purpose for retro-computing for me, is stripping out all the "modern" b.s. from my web activities when I Don't need them, or don't want to play guess-a-roo with NoScript.