mention nos2x-fox on README.

README.md

@@ -4,9 +4,9 @@
 
 ## Nostr Signer Extension
 
-This allows you to sign [Nostr](https://github.com/fiatjaf/nostr) events on web-apps without having to give them your keys.
+Use this to sign [Nostr](https://github.com/nostr-protocol/nostr) events on web-apps without having to give them your keys.
 
-It provides a `window.nostr` object which has the following methods:
+It implements [NIP-07](https://github.com/nostr-protocol/nips/blob/master/07.md), i.e. provides a `window.nostr` object which has the following methods:
 
 ```
 async window.nostr.getPublicKey(): string // returns your public key as hex
@@ -16,6 +16,8 @@ async window.nostr.nip04.encrypt(pubkey, plaintext): string // returns ciphertex
 async window.nostr.nip04.decrypt(pubkey, ciphertext): string // takes ciphertext+iv as specified in nip04
 ```
 
+This extension is Chromium-only. For a maintained Firefox fork, see [nos2x-fox](https://diegogurpegui.com/nos2x-fox/).
+
 ## Demo Video
 
 https://user-images.githubusercontent.com/1653275/149637382-65d50a85-fe30-4259-b7de-99c88b089b53.mp4