When have you last tried it, and what types of sites are you struggling with? Curious since I had the same concern in the past, but it's been a long time since it's been an issue.
Safari still seems better on battery life on macOS, but I can't really tell a difference between Chrome and Firefox anymore.
Ah, I can definitely see mobile being a different story. Google is probably pouring immense resources into performance there as it directly affects battery life, just like Apple does into Safari.
I'm unfortunately on the latter platform, so I'm limited to WebKit chrome wrappers for the time being.
If Firefox is reduced to just nerds who post in forums it's totally dead. Maybe it's at that point already.
Tbh I still use Chrome because Firefox's performance just isn't as good. I wish it weren't so but there we go.