I have found HiveKeychain to be a much more reliable and easier sign-in mechanism than HiveSigner. They have a version for Firefox, as well as another version in the ChromeStore that works for Chromium-based browsers like Brave, Opera, Chrome, and others.

If you try it, you will create a special password to open the HiveKeychain extension after installation. Then, enter your account name when promted, your Master Password, and Keychain will import all of your keys for you. You can also have multiple accounts in Keychain, so you can put your other account there, too, and quickly switch between them, effortlessly! Keychain is the best thing since sliced bread! 🙂