Try Vivaldi to get rid of those graphical issues and get true fullscreen. I use it for all my html games now and love it.
You can also get true full screen easily by pressing F11 on Firefox. We can also zoom in and out like any other browser. That one Economy page is the only screen that's broken, and mine looks fine with a bit of zooming (Or, it could be that I'm simply not making enough income to force the digits to the next line yet--looks like 3 digits is okay but 4 makes /"day" goto the next line).
It's funny that Vivaldi spun off from Opera when they adopted the Blink engine (Chromium's code) abandoning their own Presto engine, but Vivaldi also uses the Blink engine now. It's great if you like it, but it ain't for me because it's not open source, and IMHO, is just another Chromium clone with a proprietary skin and a few plugins.