Does the Google Flights link work?
I haven't been able to make it work: even though the address bar shows the fully detailed link from ITA, the page that loads is simply the Google Flights starting page (see example in attached pic).
Google doesn't publish a URL API for Google Flights as far as I know; I imagine they change the spec for it as and when they please, without documentation, so it's no surprise that the PowerTools links have broken over time.