“After some time”, not sure when exactly it occurs, let’s say ten minutes, firefox will refuse to take any keyboard input until a new window is opened.
It’s quite annoying and thought it might be due to the specific firefox version, but I’m still having this issue after having updated firefox.
[edit]
I just updated my firefox extensions.
I can imagine that it might be caused by this,
so I’ll wait and see if the problem still occurs.