From a usability perspective it's not as good as Firefox. But from a privacy stand point it's much better.
What I mean about usability is that due to it trying to prevent you from being fingerprinted it opens the browser in the same size window everytime, regardless of whether you prefer maximised or not. It has dark mode turned off. It doesn't remember cookies unless you explicitly manually add an exception. From a privacy perspective these are all good things but for convenience they're not.
All of these mild inconveniences can however be turned off if you wish. Just be aware you won't be browsing as securely then though.
As a Firefox replacement in all other regards, it's pretty much the same software. No, it is the same software.
If you use Linux and a password manager you may have an issue getting flatpaks to speak to each other and you also may have to move a folder from .mozilla to .librewolf to get them to speak to each other. These are easily searchable issues if you have them with simple fixes though.
In all other regards, to me at least, it feels just like Firefox