Quote Originally Posted by salam View Post
I am using Firefox DevTools to emulate the mobile device like Samsung S7.
That here is kind of the problem.
The Firefox DevTools aren't meant to simulate the whole browser experience you get on a mobile device. It is only meant to emulate the sizes and to a certain degree the touch functionality.
For example, nearly any mobile phone will just pop up a separate list, if you select any type of combobox. But if you use DevTools, you won't get that 'popup'. It will only do the drop-down of the list.

Just go to any website you know, that has a combobox and try it there. It won't work right with the DevTolls.