nos2x-fox is a Firefox add-on that lets you manager your Nostr keys in one place, and then sign events in websites without exposing your private key.
It also has some additional features like giving permissions to sites for a limited period of time, or to manage and save your preferred relays.
More information at the NIP-07 documentation.
Check out these important links:
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Add-on in Firefox AMO
The Add-on directly on Firefox Marketplace. -
Releases
You will find the ".xpi" files to install locally (signed by Mozilla) -
Main GitHub repo
You'll see some screenshots here, development info, and the code of course.