They are not a like for like alternative.

Profiles allow for greater separation of browsing personas: I can have a different set of passwords, extensions, bookmarks per persona I have like Work, Personal, Focus etc...

And while Firefox does have profiles, its not a great user experience. Theres no quick switching, the UI to access it feels outdated, and in general as much as it pains me to say it, Google has done a great job at implementing it.

I'm sure Firefox will get there, but as of right now its a sub-par experience.

Multi Account Containers don’t sync with Firefox Sync. I assigned hundreds of websites to various containers only to lose them all when I rebuilt my Mac. Safari, Chrome, Edge all have this functionality and until Mozilla add this, Firefox is DOA for me.