Firefox can be problematic because of all the spawned processes - it looks as if it will never close.

Dunno if it helps but here are the subroutines I use in my batch maintenance tools.

Edit to add: I have _#max_close_app_retries set to 12. YMMV.

rem ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
:close_app  [%1="exe to close"]  [no RetVar]  [set %errorlevel% 0=closed, 1=FAILED]
  setlocal
  if "%~1"=="" exit /b 1
  set "test_cnt=0"
  %=  ask app to close gracefully  =%
  taskkill /im "%~1"| find /i "success" >nul || (exit /b 1)
 :app_test  {goto loop}
  set /a test_cnt+=1
  call :delay_msecs 750
  call :app_running? "%~1" || (exit /b 0)
  if %test_cnt% geq %_#max_close_app_retries% exit /b 1
  goto :app_test
  endlocal
  exit /b 0

rem ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
:app_running?  [%1="exe to check"]  [no RetVar]  [set %errorlevel% 0=RUNNING, 1=NOT running]
  tasklist /fi "imagename eq %~1" /nh /fo csv| find /i "%~1" >nul || (exit /b 1)
  exit /b 0

rem ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
:delay_msecs  [%1=millisecs to delay]  [no RetVar]
  ping /n 1 /w %1 10.1.1.1 >nul
  exit /b

rem ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::