I just started using Firefox Nightly and I’m really liking it. Daily updates, more customization, access to new features (2 full versions ahead of vanilla Firefox).
It feels faster to me but I audited it and it’s actually ever so slightly slower than regular Firefox.
Only two drawbacks – 1) you have to manually give some extensions needed permissions and 2) it makes your browser easier to fingerprint because fewer people use Firefox Nightly.