Display issue?

I spent the better part of 2 hours putting together the first page of my campaign only to have most of it randomly disappear. I've tried closing my browser (firefox) and restarting my laptop, zooming in and out, etc. but nothing seems to work. Weirdly, in the little preview in the page toolbar everything shows up (see screenshot)! This all happened after I created a new page and found I couldn't drag anything onto it. I'm probably missing something obvious, but HALP!!!

To clarify: what has gone missing? - Gauss

The map image, I think. I've had this happen to me sometimes too, with Chrome, but generally reloading has helped fix it for me. What happens is the map and background layer goes white and only leaves GM and Token layer stuff.