Work in Mosaico is easily lost
There is a point of potentially horrible user experience when working with Mosaico mailings where a user's work can be lost with an inadvertent click of the mouse. There is no warning or recourse or ability to recover the work.
Within the Mosaico editor, when a user wants to switch between blocks, content, or style, those selections are immediately below the Civi Menu (this may apply only to Joomla). A user can easily move the mouse pointer one pixel too high into the menu, shift the pointer back down to the Mosaico interface quickly and click, but the brief hovering over the menu has triggered a submenu which covers the Mosaico interface and is the element that receives the click. This happens too quickly for the user to withhold their intended click. Consequently, the menu choice is loaded in the browser, losing any unsaved work in Mosaico.
One possible fix is to hide the navbar when within the Mosaico editor, as there is no reason to need it in that context.