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I don't have an up to date tutorial, but it is really easy.

Look in the extension store for Hive Keychain, make sure it is the one from @yabapmatt and install it.

Once installed, it will prompt you to set a password, you will need this to unlock the extension. From there you can add your account(s) and it will manage authenticating to Hive services for you.

I do recommend setting the idle lock-in the preferences to lock the extension when you are not using it. It tends to lock even when you are using it though after a set time.

If you still have questions, let me know and I can make a newer tutorial.

Thanks so much, this is extra helpful and I feel really silly for not checking on github first before asking you :)
I appreciate your time!

You don't want to use GitHub, it is now on the Chrome Web Store (for Chrome and Brave) and on the Firefox store for Firefox, I recommend going directly there.