Options page turn black

I currently have 11 short keys. Every time I add one more, total 12, the option page edit box turns black. I need to uninstall the plugin to be able to get back to the 11 short keys, and make it work again.

Using the Firefox port 1.9.5 on 78.7.1esr (64-bit)

Just noticed that it's screen resolution related. I don't have this issues on my larger screen!