karabiner-elements setting: F5 to CMD+R key (browser only) vi ~/.config/karabiner/assets/complex_modifications/browser.json

browser.json

{
  "title": "browser",
  "conditions": [
    {
      "type": "frontmost_application_if",
      "bundle_identifiers": [
        "^com\\.apple\\.Safari",
        "^com\\.google\\.Chrome",
        "^com\\.vivaldi\\.Vivaldi"
      ]
    }
  ],
  "rules": [
    {
      "description": "F5 to reload",
      "manipulators": [
        {
          "type": "basic",
          "from": {
            "key_code": "f5"
          },
          "to": [
            {
              "key_code": "r",
              "modifiers": ["command"]
            }
          ]
        }
      ]
    }
  ]
}