Environment: 7.5 Mobile Web Desk
In Mobile WebDesk it does not appear possible to zoom in/out of screen. For example, on a smartphone using 2 fingers to zoom in/out.
Mobile Web Desk is developed in JQuery Mobile. JQuery Mobile is designed to look like a smartphone app which has been suitably scaled for a mobile device. On some platforms, there is a bug that will incorrectly scale the page when you change orientation which is why JQuery disabled the zoom feature.