Chrome 73 was pushed last week in WebPageTest (I marked with an annotation), Firefox and Chrome updated with WebPageReplay the 19th of March.
One thing I think we can say so far is that FF 66 seems to give us faster onLoad for some pages (this is enwiki/Facebook):
I'll do a summary of metric changes later this week when latest FF is on WPT and I got more time to look at the Chrome metrics.