This is an awesome tip!!
Is there a way to do it without signing, ie backing up just public data? I’m still feeling pretty monogamous about my nsec and haven’t put it in any extensions yet 😉
Pro #Nostr Tip: Visit https://metadata.nostr.com to backup and download your profile data! Sometimes here on nostr you'll come across a client that acts a little wonky and does something it shouldn't do, such as blow away your contact list. If this were to happen, you can visit this website to easily restore everything, if and only if you made a backup first.
Discussion
i'd say that nos2x, nostr connect, and alby are pretty safe. they don't send your extensions anywhere. it's just stored in local browser data. you could always nuke the extension afterwards.