Firefox PDF viewer on desktops has "Presentation mode" which I'm using from time to time to show my slides. I suggest to add possibility to zoom PDF while presenting which, at leats I’m, missing a lot (via CTRL+mousewheel and CTRL+plus/minus).
ATM I'm using other pdf viewers to achieve it and it would be great to have it in FF since browsers becoming common alternative for opening these files. Also FF is investing in better PDF comparability and this would be a nice feature (as much as I checked none of browsers has this feature yet).