How did you actually measure this? I wonder whether these small timing differences may just be differences in how the respective dev tools report the timing info.
FWIW I also don't think the relative difference will be this large for bigger sites - I'd be very surprised if a site that takes 1s to load in Chrome would take 1.5-2s in Firefox.
So once the page is loaded, JS performance seems to be about on par, but page loads are faster in Chrome.
To measure I just used dev tools. But there is quite a lot of randomness involved -- sometimes the engine scheduling planets align, and sometimes they are way out of alignment. You'd need thousands of samples or more to get an accurate reading. I just refreshed a few times to get ballpark numbers.
From pressing enter to the browser initiating a fetch was around 16ms.
Chrome takes 102-200ms to render the page, Firefox takes 150-400ms. 1.5 to 2x slower -- and that's after all the performance upgrades they've done with Rust and Quantum.
Network inspector says Firefox is spending 150-270ms "blocked" before it even initiates the connection. On Chrome the block is 3-18ms (15-50x (!!) faster).
There's also UI lag. When I press Ctrl+N, I expect a new window to open immediately. Chrome and Chromium based browsers do that. I cannot even perceive the delay between pressing Ctrl+N and a new window appearing. With Firefox it takes about 0.5-1 seconds before anything happens at all. This seems to be another 10-20x difference (though I'd have to record my screen and measure the difference).
Curiously, Re: UI lag, I think the actual time until the navbar is usable is about the same. But Firefox waits until the whole window is built before it displays it, while Chrome opens the window immediately and fills it in. From a user experience (I do command, I expect feedback) this makes a huge difference.
I switch back to Firefox roughly once a year after reading how fast it's gotten. But I have been disappointed on this front every single time. I want Firefox to succeed, I really do. I am donating to Mozilla every month. But as it is right now, I can't tolerate such lag, for a trivial action I perform thousands of times a day.