Clean up extension polyfill abstraction

app/scripts/contentscript.js

@@ -9,14 +9,19 @@ if (shouldInjectWeb3()) {
 }
 
 function setupInjection(){
-  // inject in-page script
-  var scriptTag = document.createElement('script')
-  var urlGetter = extension.extension || chrome.extension
-  scriptTag.src = urlGetter.getURL('scripts/inpage.js')
-  scriptTag.onload = function () { this.parentNode.removeChild(this) }
-  var container = document.head || document.documentElement
-  // append as first child
-  container.insertBefore(scriptTag, container.children[0])
+  try {
+
+    // inject in-page script
+    var scriptTag = document.createElement('script')
+    scriptTag.src = extension.extension.getURL('scripts/inpage.js')
+    scriptTag.onload = function () { this.parentNode.removeChild(this) }
+    var container = document.head || document.documentElement
+    // append as first child
+    container.insertBefore(scriptTag, container.children[0])
+
+  } catch (e) {
+    console.error('Metamask injection failed.', e)
+  }
 }
 
 function setupStreams(){

app/scripts/lib/extension-instance.js

@@ -24,14 +24,9 @@ const apis = [
 
 function Extension () {
   const _this = this
-  let global = window
-
-  if (window.chrome) {
-    global = window.chrome
-  }
 
   apis.forEach(function (api) {
-    _this[api] = global[api]
+    _this[api] = chrome ? chrome[api] : window[api] || browser.extension[api]
   })
 }