User Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:54.0) Gecko/20100101 Firefox/54.0 Build ID: 20170608105825 Steps to reproduce: Enable Responsive Design Mode, select a device, activate the TOUCH SIMULATION mode. Actual results: All select lists now refuse to drop-down themselves when clicked (or touched). Expected results: Select options should've been shown as with regular clicks (no touch simulation mode). This happens on all websites, therefore, it's not a problem with my app.

Thanks for filing this! I would guess that the touch simulator's handling of mouse events prevents the `mozshowdropdown` event from being sent, blocking the drop down list from being shown. Changing to a more realistic mobile simulation through something like bug 1282089 would be a nice way to resolve this.