Switched from Chrome to Nightly as my main browser 2 days ago when KeepassHttpConnector [0] got it's 1.0 release. Speed is absolutely on par with Chrome (which is something I never had in my earlier tries, usually gave FF a chance 2 times per year). Had 1 full browser crash which never happened with Chrome (in recent years), but then I was also running stable vs nightly now.
I'm still missing one extension (Join for Android), but I can live without it for now and might actually just help joaoapps in developing it.
One thing that annoyed me was the large min tab size as I didn't like scrolling tabs. Someone on Reddit pointed me to the right userChrome.css tweak though [1]
Overall I'm pretty happy being back on Firefox after many, many years.
[0]: https://github.com/smorks/keepasshttp-connector/releases
[1]: https://github.com/Timvde/UserChrome-Tweaks/blob/master/tabs...