Browser extensions allow you to customize your web browser to tweak your web browser to look and behave how you want. In this talk we will explore building extensions that work across web browsers and operating systems and ways to overcome challenges caused by cross-browser differences.

As we walk through extension code samples, we will discuss the motivations for our design decisions and provide guidance for building robust, cross-browser, cross-platform extensions. We cover several aspects of reliable extension design including background scripts, user interaction, host permissions and manifest version 2/3 in Firefox and Chrome. After this talk, you will be able to build browser extensions for Firefox, Firefox for Android, and Chrome.