Firefox WebExtension support

shells/chrome/devtools-background.html

@@ -1 +1,2 @@
+<meta charset="utf-8">
 <script src="./build/devtools-background.js"></script>

shells/chrome/manifest.json

@@ -1,7 +1,7 @@
 {
   "name": "Vue.js devtools",
   "version": "3.1.3",
-  "description": "Chrome devtools extension for debugging Vue.js applications.",
+  "description": "Chrome and Firefox DevTools extension for debugging Vue.js applications.",
   "manifest_version": 2,
   "icons": {
     "16": "icons/16.png",

shells/chrome/popups/disabled.html

@@ -1,3 +1,4 @@
+<meta charset="utf-8">
 <p style="width: 200px">
   Vue.js is detected on this page.
   Devtools inspection is not available because it's in

shells/chrome/popups/enabled.html

@@ -1,4 +1,5 @@
+<meta charset="utf-8">
 <p style="width: 180px;">
   Vue.js is detected on this page.
-  Open Chrome Devtools and look for the Vue panel.
+  Open DevTools and look for the Vue panel.
 </p>

shells/chrome/popups/not-found.html

@@ -1,3 +1,4 @@
+<meta charset="utf-8">
 <p style="white-space: nowrap">
   Vue.js not detected
 </p>

shells/chrome/webpack.config.js

@@ -3,7 +3,7 @@ var webpack = require('webpack')
 var alias = require('../alias')
 
 var bubleOptions = {
-  target: process.env.NODE_ENV === 'production' ? null : { chrome: 52 },
+  target: process.env.NODE_ENV === 'production' ? null : { chrome: 52, firefox: 48 },
   objectAssign: 'Object.assign'
 }
 

shells/dev/webpack.config.js

@@ -4,7 +4,7 @@ var alias = require('../alias')
 var FriendlyErrorsPlugin = require('friendly-errors-webpack-plugin')
 
 var bubleOptions = {
-  target: { chrome: 52 },
+  target: { chrome: 52, firefox: 48 },
   objectAssign: 'Object.assign'
 }