background script not getting executed in firefox extension but gets detected when temporarily load extension

I have written this manifest.json

{
  "manifest_version": 2,
  "name": "Get tab url and title",
  "description": "Copies the Title and URL of the currently selected tab",
  "version": "0.0.1",
  "icons": {
    "48": "icon.png"
  },
  "permissions": ["tabs", "contextMenus", "clipboardWrite"],
  "background": {
    "scripts": ["background.js"]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "[email protected]"
    }
  },
  "content_scripts": [],
  "browser_action": {
    "default_icon": {
      "48": "icon.png"
    }
  }
}

and I have also added background.js script as well

cat background.js 
alert("Hello from the other side!!!");

for the time being I just added alert so that when the extension is clicked I should get to see alert prompt.

see the extension is loaded;