I have suspicion that lots of the "chrome is faster" is because devs optimise for chrome. More unique and "new" the API is the bigger the difference. Webgl is probably pretty different between browsers but nobody will bother to even look at webgl project in Firefox. It's pretty remarkable that such complex code can run pretty well in multiple different browsers.

Another example Chrome has rel=prerender support and some libraries use it to make loading pages faster. Safari and Firefox don't support it. But it's progressive enhancement so why not use it. Result is that Chrome seems faster. There are probably many ways to make things faster on the other side but nobody will bother.