Buttercup by MadDev

Manage your online identities and credentials with Buttercup: An open-source, free and secure credentials manager. Buttercup uses the strongest industry techniques to encrypt and store your details in a variety of locations of your choosing. Use My Buttercup, Google Drive, Dropbox, WebDAV or local files (via the Desktop app) to remotely or locally access your vault. Save new logins to your secure archives.

The vault management interface allows for full control over your vault's contents, so it can even be used as a stand-alone application. Create and edit different item types (logins, websites, credit-cards, notes etc.) and even attach securely-encrypted files.

Please note that this extension does not support Android platforms.