The Alby Browser Extension is an application that runs only in your browser. It doesn't share your keys with any other app. That's why you can use it for Nostr key management.

Nostr | Browser Extension | Alby Guides
Nostr is a simple and open protocol that aims to create censorship-resistant social networks and works with cryptographic keys. Use Alby to securel...
When you enter an nsec into @Fountain or @Alby or @npub1tnpf...kkpe extension, do they see it or not?
Where is it stored?
Why do people say it isn’t a good idea to enter one’s nsec into many apps?
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