Because if firefox hadn't nuked the user's config we wouldn't be talking about how to recover that config. Any time the advice is "restore from backups" then the product has exhibited a poor user experience. And this isn't because of some hardware failure, this is just the software bungling an update flow, with no special notice to the user or any obvious way to recover.
I do. I've learned over the years that any MS update could nuke my computer. And what I'm saying is on subject, you have no proof that Mozilla nuked the configuration. It could have been caused by circumstances outside their control. I've been using FF for years and years and never lost anything, presumably including after this so-called failed update.