Or get Lightshot and you just press the application icon or something with FH open, then everything will be grey, just click and move the mouse, then click on the cloud icon when you have done the rectangle right and it uploads instantly! blablabla
It seems like a graphics problem... are you using FH packed by Shell Prisoner for Macs? It's known that it has some glitches related to crashing etc etc. I suggest switching to OpenGL, I don't have a Mac so I don't know how is the FH directory in Mac (I'm assuming it's the same but without a few dlls and such, I honestly have no idea and I don't want to confuse people).
If OpenGL doesn't work, then go for the last step: WINE. Basically, you download this program and download the FH for Windows and then open WINE and search for the executable and it will run. I don't know how WINE works, since, like I said, I don't have a Mac neither a Linux. I'm sure WINE is more stable than the "official" FH for Mac, but I'm sure it will give some graphics problems still.
Anyways, good luck with that. If neither options works then I think you must get a Windows computer if you have the money and really want to play FH (and other non-Mac compatible programs).