Examine source code of Right click is standard.

{
  "manifest_version": 2,
  "name": "Right click is standard.",
  "version": "1.0",
  "description": "Causes external links in JIRA Cloud (any *.atlassian.net address) to open in a new window / tab.  This is in response to JIRACLOUD-9380 where Atlassian doesn't appear to be taking any action on the matter (since 2006!).",
  "icons": {
    "48": "mouse-black-18dp.svg"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.atlassian.net/*"
      ],
      "js": [
        "jquery-3.5.1.min.js",
        "external_link.js"
      ]
    }
  ]
}