I faced this issue in both Google Chrome and Firefox on 18.10. When I was trying on forums like this, suddenly keystrokes make no difference. Nothing gets typed. Even refreshing the page is not helping. After some time it gets ok by itself. Anyone else facing this issue ? It's quite annoying. It happened twice when I was typing this problem here.
I am using 18.10 with Dash to Panel extension. Otherwise, everything is 18.10 stock.
This happens with both the laptop keyboard and an external USB keyboard.