Firefox does not open when debugging in Visual Studio Code

When I start debugging with my launch configuration for Chrome, the browser opens. But when I use my launch configuration for Firefox, the browser does not open. A Firefox process is started though. There are no error messages.

• Visual Studio Code 1.36.1
• Debugger for Firefox 1.8.1
• Firefox 68.0.1
• Windows 10 1803
• Angular 7.0.0 (should not matter)

.vscode/launch.json:

{
    "version": "0.2.0",
    "configurations": [
      {
        "type": "chrome",
        "request": "launch",
        "name": "Chrome + localhost",
        "url": "http://localhost:4200",
        "webRoot": "${workspaceFolder}"
      },
      {
        "type": "firefox",
        "request": "launch",
        "reAttach": true,
        "name": "Firefox + localhost",
        "url": "http://localhost:4200",
        "webRoot": "${workspaceFolder}"
      },
    ]
  }