Eight Dollars for Firefox v1.1
Due to Twitter discontinuing the the actual verification program, this add-on is now deprecated. All accounts with a blue verification badge are not actually verified, just have the premium subscription, that they either paid for, or recieved for free.
Eight Dollars for Firefox can help you tell the difference between actual verified accounts and twitter blue users. Just install the extension and see the difference. Made by Will Seagar and Walter Lim, ported to Firefox by Hexandcube.