Re-add support for Firefox keys -, + and ;

manifest.json

@@ -1,7 +1,7 @@
 {
   "name": "Video Speed Controller",
   "short_name": "videospeed",
-  "version": "0.5.9",
+  "version": "0.5.9.1",
   "manifest_version": 2,
   "description": "Speed up, slow down, advance and rewind any HTML5 video with quick shortcuts.",
   "homepage_url": "https://github.com/codebicycle/videospeed",

options.js

@@ -75,6 +75,9 @@ var keyCodeAliases = {
   220: '\\',
   221: ']',
   222: '\'',
+  59:  ';',
+  61:  '+',
+  173: '-',
 }
 
 function recordKeyPress(e) {