how to run firefox without a window?

i know firefox headless mode but we can't run normal firefox after that

firefox doesn't has hwnd on every window so i can't hide it using c++. It's possible using mozila window class but i wanna hide a specific window

    STARTUPINFO si;
PROCESS_INFORMATION pi;

    ZeroMemory( &si, sizeof(si) );
    si.cb = sizeof(si);
    ZeroMemory( &pi, sizeof(pi) );


    CreateProcess((GetDefaultBrowser()).c_str(),NULL,NULL,NULL,FALSE,CREATE_NEW_CONSOLE,NULL,NULL,&si,&pi);
    CloseHandle( pi.hProcess );
    CloseHandle( pi.hThread );

anyone know how to fix this ;(.

i hope it can be done just using c++.
pls specify reason to downvote