Karabiner-Elements

disable-cmd-q-for-firefox.json

{
  "title": "Disable Cmd-q for FireFox",
  "rules": [
    {
      "description": "Disable Cmd-q for FireFox",
      "manipulators": [
        {
          "conditions": [
            {
              "bundle_identifiers": [ "org\\.mozilla\\.firefoxdeveloperedition" ],
              "type": "frontmost_application_if"
            }
          ],
          "from": {
            "key_code": "q",
            "modifiers": { "mandatory": [ "left_command" ] }
          },
          "to": [ ],
          "type": "basic"
        }
      ]
    }
  ]
}

right-cmd-as-F19-change.json

{
  "title": "Change right_command key to F19",
  "rules": [
    {
      "description": "Change right_command key to F19 (Use it as language change key)",
      "manipulators": [
        {
          "type": "basic",
          "from": {"key_code": "right_command"},
          "to": [{"key_code": "f19", "repeat": false}]
        }
      ]
    }
  ]
}