Chrome 49 is bringing support for CSS custom properties to make it easy to define property variables in CSS, background sync support with service workers, improved ECMAScript 2015 support, the keygen element to generate a key-pair as part of an HTML form, a new MediaRecorder API for recording a user's audio and video without the use of any plugins, WebAudio API additions, and a variety of other enhancements.
More details on the just-released Chrome 49 Beta can be found via the Chromium.org blog.
Meanwhile, the Mozilla team today announced the release of Firefox 46 Developer Edition. Firefox Developer Edition 46 adds new memory profiling features, a new performance tool, an EmScripten demangling feature, and other enhancements. Those Firefox Developer Edition 46 features are explained in more detail via hacks.mozilla.org.