Browsers in 2016 do vastly more than they did in 2006, websites are richer and are much closer to apps than static pages.
The demand that "I want my browser to be exactly the same speed as it used to be, but also support all these new features" doesn't seem like a reasonable engineering ask. You optimize for the hardware that people will run, not the hardware of 10 years ago, and you also optimize for your slowest new use cases, not the old use cases which will be fast enough even without much optimization.
The argument also doesn't make logical sense. Ten years ago, there was someone saying software 'largely do pretty much the same things' compared to 1996, and ten years before that I'm sure someone was comparing 1996 software to 1986 and saying something similar. But software today looks nothing like in 1986.