CreateProcessW

function StartFirefox(Firefox, URL: string): Boolean;
var
 si: TStartupInfo;
 pi: TProcessInformation;
begin
ZeroMemory(@si,sizeof(si));
si.cb := SizeOf(si);
si.dwFlags:=STARTF_USESHOWWINDOW;
si.wShowWindow:=SW_SHOWMAXIMIZED;
result:=CreateProcessW(LPWSTR(Firefox), LPWSTR(URL), nil, nil, False, 0, nil, nil, SI, PI);
//StartFirefox('c:\Program Files\Firefox Developer Edition\firefox.exe',string.empty);//применение
end;