WebExtensions port Minimum Viable Product. Works in Firefox

- comment out chrome.extension.sendMessage
- rename chrome.storage.sync to chrome.storage.local
- remove createShadowRoot
- add reload_once function

manifest.json

@@ -4,7 +4,7 @@
   "version": "0.4.2",
   "manifest_version": 2,
   "description": "Speed up, slow down, advance and rewind any HTML5 video with quick shortcuts.",
-  "homepage_url": "https://github.com/igrigorik/videospeed",
+  "homepage_url": "https://github.com/codebicycle/videospeed",
   "icons": {
     "16": "icons/icon16.png",
     "48": "icons/icon48.png",