Firefox 55 for developers - Mozilla | MDN

Firefox 55 is out this week and brings Background Tasks API (requestIdleCallback), WebVR 1.1, the Intersection Observer API, a whole lot of fixes, additions and updates to existing features. This version finally restricts Geolocation API, and Storage API to secure contexts (HTTPS), allows mixed content for localhost, and makes Flash click-to-activate by default and restricts the plugin to only be loaded by the http:// and https:// scheme. On Linux, you can now run Firefox in headless mode with the -headless flag.