Issue 6620 - Update extension description

_locales/en_US/messages.json

 {
   "add": {
     "description": "This is the label for the 'Add' buttons.",
     "message": "Add"
   },
   "add_filters_msg": {
     "message": "Add filter(s)?"
   },
   "block_element": {
     "description": "Context menu item that adds a filter which blocks the selected element",
     "message": "Block element"
   },
   "cancel": {
     "description": "Cancel button label",
     "message": "Cancel"
   },
   "clickhide_instructions": {
     "description": "Instructions shown in popup UI before it disapears, when \"Block element\" action is executed",
     "message": "After closing this popup, click (or right-click) an element on the page."
   },
   "description": {
     "description": "Note: this cannot be longer than 132 characters",
-    "message": "With over 500 million downloads, Adblock Plus is the one of the world's most popular ad blockers."
+    "message": "With over 500 million downloads, Adblock Plus is one of the world's most popular ad blockers."
   },
   "disabled_for_site":
   {
     "description": "Popup balloon label to disable blocking",
     "message": "<strong>Disabled</strong> on this site"
   },
   "easy_create_filter": {
     "description": "Action in popup UI to add a filter which blocks an element selected from the current page",
     "message": "Block element"
   },
@@ skipping 106 matching lines @@
     }
   },
   "continue": {
     "description": "Continue button label",
     "message": "Continue"
   },
   "sendReport": {
     "message": "Report issue on this page"
   }
 }