Live editing Menu Module, can't see the mobile menu while Responsive editing

Use Case: While I’m using the Menu Module in Themer, I assume it responds the same way whether it’s in a Themer Header or just in a page.
Problem: When editing a Menu Module, once I get to the screen size where it’s set to go to Responsive (Mobile and often Tablet) I lose the live preview of the Nav Menu while editing (except the Hamburger toggle itself). I swore there used to be a trick to get the menu to drop down and show itself for live editing (to tweak padding, line height etc.). I’m having to go out to “P” each time just to see how it looks, which is
annoying and inefficient. Tried of Firefox too in case it was a Chrome issue - same problem on both.