If you click on dropdown menu only once it should open it and wait for user to choose which item to select. That works on chromium based browsers.
But on Firefox if you click on dropdown menu once it will already execute on change event instead of wait for user to choose item from drop down menu.
If I click and hold mouse I can hover to another item and then release the mouse to choose and item (That works on Firefox) but I know that most users won’t know how to use that system.
So this is one of the major bugs FireFox needs to fix it immediately as drop downs are so popular now days.
You can try it by yourself on this extension: https://addons.mozilla.org/en-US/firefox/addon/passky/