Inject automatically on install etc., add mime types, and fix nits.

go-back-with-backspace/_locales/en/messages.json

Index: go-back-with-backspace/_locales/en/messages.json
diff --git a/go-back-with-backspace/_locales/en/messages.json b/go-back-with-backspace/_locales/en/messages.json
index 4649c0517c73e5bbc13e97271887322e415c7f2f..481193a4b90b594c41de0e01f9432b65c01471d4 100644
--- a/go-back-with-backspace/_locales/en/messages.json
+++ b/go-back-with-backspace/_locales/en/messages.json
@@ -7,18 +7,6 @@
     "message": "Re-enables the backspace key as a back navigation button (except when writing text).",
     "description": "Brief description of this extension."
   },
-  "installedTitle": {
-    "message": "Go Back With Backspace Installed",
-    "description": "title of the installation notes page shown on first installation."
-  },
-  "installedHeading": {
-    "message": "Go Back With Backspace installation notes",
-    "description": "Page heading for the installation notes page."
-  },
-  "installedNotes": {
-    "message": "Thank you for installing the \"Go Back With Backspace\" extension. After this extension is newly installed, enabled, or updated, any open tabs will need to be reloaded for the changes to take effect.",
-    "description": "Content of the installation notes page, explaining how to get the extension to workimmediately after installation."
-  },
   "optionsTitle": {
     "message": "Go Back With Backspace Options",
     "description": "Used in the page title and top heading of the options page."
@@ -104,7 +92,7 @@
     "description": "Initial body of the feedback email created by the 'Send feedback' button in places where there is no relevant URL (e.g., the installation notes page)."
   },
   "reportBodyWithURL": {
-    "message": "The extension doesn't do the right thing on the page at\n$URL$.\n\nAdd any details below. Which part of the page doesn't work properly? We won't be able to respond to every piece of feedback individually, but we appreciate your time and thoughts.)",
+    "message": "The extension doesn't do the right thing on the page at\n$URL$.\n\nAdd any details below. Which part of the page doesn't work properly? (We won't be able to respond to every piece of feedback individually, but we appreciate your time and thoughts.)",
     "description": "Initial body of the feedback email created by the 'Send feedback' button in places where we have a relevant URL (e.g. the browser action popup).",
     "placeholders": {
       "url": {