Only a very bad person would put the crappy performance of Google products in non-Google browsers down to anything nefarious. Really, they just don't care ;-)
I... don't understand why you'd project that viewpoint on me. It's quite a bit easier to imagine that there are things Chrome or Edge are doing that are not as well optimized on Firefox (or vice versa, of course).
There's 3 separate engines all with different tradeoffs.
Have you used Firefox in the past couple of years?
Even if it were slow (which it isn't), it's not doing surveillance for money. If you really want a Chromium-based browser, you could always use Vivaldi or Opera or take your pick of many others.
And the recent buzz about a concurrent engine shows how much slower. When you have 300%+ headroom just by uncoupling your execution strategy from an unnecessary global lock no one else has, you are not "speeding up". You are "catching up."
I have a Surface Book, a recent Macbook Pro, and homebuilt Windows machine with components sourced from 2015's crop with an eye towards performance. Even if it were the case that I was using older hardware, this wouldn't exactly be a good story for Firefox.
Firefox is sluggish on every machine, and consistently feels like the slower paint. I understand the synthetic benchmarks are not so distant, but we don't interact with browsers at the level of Sunspider benchmarks. We interact at the level of full dom renders to screen, first clicks available, scrolling and repainting performance, tab open and close time, and startup time.
Firefox has never been a positive experience for me on those on anything but the very oldest of Linux boxes, and quite frankly I've written off the entire X11/Linux desktop environment as a tire fire with people trapped inside.
Chrome does a really good job hiding that the page is still loading, because it's multithreaded and doesn't cause the UI to seize while the page is loading. Firefox is FINALLY starting to work on this.
Also, note the 12 second time is what the Google+ team clocked as average. Yours may have been faster. Others, were even slower.
I know Firefox was terribly slow there (like it is with many script-driven websites), but I never dug into why.