See the component page for more information.
Make sure you import the right element definition (dist/facebook-login.html)
This Polymer element is written in ECMAScript 15. The repository includes a gulpfile that uses babel and other tools to transcompile the ECMAScript 15 code to ECMAScript 5 code. If you want to contribute, run gulp in your terminal to build the dist directory and compile the element for browsers that lack support for ES15.
Clone this repository inside a wrapper folder (i.e. mkdir facebook-login-wrapper && cd $_ && git clone https://github.com/davidwittenbrink/facebook-login.git) to avoid bower from installing dependencies inside your workspace (the will be installed inside the wrapper folder instead).
Run npm start to install devDependencies and bower dependencies.